TY - JOUR A1 - Sanjurjo-Ferrrin, G. A1 - Torrejon, J. M. A1 - Postnov, K. A1 - Oskinova, Lida A1 - Rodes-Roca, J. J. A1 - Bernabeu, Guillermo T1 - XMM-Newton spectroscopy of the accreting magnetar candidate 4U0114+65 JF - Astronomy and astrophysics : an international weekly journal N2 - Methods. We analysed the energy-resolved light curve and the time-resolved X-ray spectra provided by the EPIC cameras on board XMM-Newton. We also analysed the first high-resolution spectrum of this source provided by the Reflection Grating Spectrometer. Results. An X-ray pulse of 9350 +/- 160 s was measured. Comparison with previous measurements confirms the secular spin up of this source. We successfully fit the pulse-phase-resolved spectra with Comptonisation models. These models imply a very small (r similar to 3 km) and hot (kT similar to 2-3 keV) emitting region and therefore point to a hot spot over the neutron star (NS) surface as the most reliable explanation for the X-ray pulse. The long NS spin period, the spin-up rate, and persistent X-ray emission can be explained within the theory of quasi-spherical settling accretion, which may indicate that the magnetic field is in the magnetar range. Thus, 4U0114+65 could be a wind-accreting magnetar. We also observed two episodes of low luminosity. The first was only observed in the low-energy light curve and can be explained as an absorption by a large over-dense structure in the wind of the B1 supergiant donor. The second episode, which was deeper and affected all energies, may be due to temporal cessation of accretion onto one magnetic pole caused by non-spherical matter capture from the structured stellar wind. The light curve displays two types of dips that are clearly seen during the high-flux intervals. The short dips, with durations of tens of seconds, are produced through absorption by wind clumps. The long dips, in turn, seem to be associated with the rarefied interclump medium. From the analysis of the X-ray spectra, we found evidence of emission lines in the X-ray photoionised wind of the B1Ia donor. The Fe K alpha line was found to be highly variable and much weaker than in other X-ray binaries with supergiant donors. The degree of wind clumping, measured through the covering fraction, was found to be much lower than in supergiant donor stars with earlier spectral types. Conclusions. The XMM-Newton spectroscopy provided further support for the magnetar nature of the neutron star in 4U0114+65. The light curve presents dips that can be associated with clumps and the interclump medium in the stellar wind of the mass donor. KW - X-rays: binaries KW - stars: winds, outflows KW - pulsars: individual: 4U0114+65 Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201630119 SN - 1432-0746 VL - 606 SP - 4039 EP - 4042 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Ignace, Richard A1 - Oskinova, Lida A1 - Brown, John C. T1 - XMM-Newton Observations of the Nitrogen-Rich Wolf-Rayet star WR1 N2 - We present XMM-Newton results for the X-ray spectrum from the N-rich Wolf-Rayet (WR) star WR 1. The EPIC instrument was used to obtain a medium-resolution spectrum. The following features characterize this spectrum: (a) significant emission "bumps" appear that are coincident with the wavelengths of typical strong lines, such as Mg XI, Si XIII and S XV; (b) little emission is detected above 4 keV, in contrast to recent reports of a hard component in the stars WR 6 and WR 110 which are of similar subtype; and (c) evidence for sulfur K-edge absorption at about 2.6 keV, which could only arise from absorption of X-rays by the ambient stellar wind. The lack of hard emission in our dataset is suggestive that WR 1 may truly be a single star, thus representing the first detailed X-ray spectrum that isolates the WR wind alone (in contrast to colliding wind zones). Although the properties of the S-edge are not well-constrained by our data, it does appear to be real, and its detection indicates that at least some of the hot gas in WR 1 must reside interior to the radius of optical depth unity for the total absorptive opacity at the energy of the edge. Y1 - 2003 ER - TY - JOUR A1 - Sidoli, Lara A1 - Sguera, Vito A1 - Esposito, Paolo A1 - Oskinova, Lida A1 - Polletta, Maria del Carmen T1 - XMM-Newton discovery of very high obscuration in the candidate Supergiant Fast X-ray Transient AX J1714.1-3912 JF - Monthly notices of the Royal Astronomical Society N2 - We have analysed an archival XMM-Newton EPIC observation that serendipitously covered the sky position of a variable X-ray source AX J1714.1-3912, previously suggested to be a Supergiant Fast X-ray Transient (SFXT). During the XMM-Newton observation the source is variable on a timescale of hundred seconds and shows two luminosity states, with a flaring activity followed by unflared emission, with a variability amplitude of a factor of about 50. We have discovered an intense iron emission line with a centroid energy of 6.4 keV in the power law-like spectrum, modified by a large absorption (N-H similar to 10(24) cm(-2)), never observed before from this source. This X-ray spectrum is unusual for an SFXT, but resembles the so-called 'highly obscured sources', high mass X-ray binaries (HMXBs) hosting an evolved B[e] supergiant companion (sgB[e]). This might suggest that AX J1714.1-3912 is a new member of this rare type of HMXBs, which includes IGR J16318-4848 and CI Camelopardalis. Increasing this small population of sources would be remarkable, as they represent an interesting short transition evolutionary stage in the evolution of massive binaries. Nevertheless, AX J1714.1-3912 appears to share X-ray properties of both kinds of HMXBs (SFXT versus sgB[e] HMXB). Therefore, further investigations of the companion star are needed to disentangle the two hypothesis. KW - X-rays: binaries KW - X-rays: individual: AX J1714.1-3912 Y1 - 2022 U6 - https://doi.org/10.1093/mnras/stac691 SN - 0035-8711 SN - 1365-2966 VL - 512 IS - 2 SP - 2929 EP - 2935 PB - Oxford Univ. Press CY - Oxford ER - TY - CHAP A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Feldmeier, Achim T1 - X-raying clumped stellar winds N2 - X-ray spectroscopy is a sensitive probe of stellar winds. X-rays originate from optically thin shock-heated plasma deep inside the wind and propagate outwards throughout absorbing cool material. Recent analyses of the line ratios from He-like ions in the X-ray spectra of O-stars highlighted problems with this general paradigm: the measured line ratios of highest ions are consistent with the location of the hottest X-ray emitting plasma very close to the base of the wind, perhaps indicating the presence of a corona, while measurements from lower ions conform with the wind-embedded shock model. Generally, to correctly model the emerging Xray spectra, a detailed knowledge of the cool wind opacities based on stellar atmosphere models is prerequisite. A nearly grey stellar wind opacity for the X-rays is deduced from the analyses of high-resolution X-ray spectra. This indicates that the stellar winds are strongly clumped. Furthermore, the nearly symmetric shape of X-ray emission line profiles can be explained if the wind clumps are radially compressed. In massive binaries the orbital variations of X-ray emission allow to probe the opacity of the stellar wind; results support the picture of strong wind clumping. In high-mass X-ray binaries, the stochastic X-ray variability and the extend of the stellar-wind part photoionized by X-rays provide further strong evidence that stellar winds consist of dense clumps. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18133 ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Oskinova, Lida A1 - Gonzalez-Galan, Ana A1 - Guerrero, Martín A. A1 - Ignace, R. A1 - Pohl, Martin T1 - X-RAY OBSERVATIONS OF BOW SHOCKS AROUND RUNAWAY O STARS. THE CASE OF zeta OPH AND BD+43 degrees 3654 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Non-thermal radiation has been predicted within bow shocks around runaway stars by recent theoretical works. We present X-ray observations toward the runaway stars zeta Oph by Chandra and Suzaku and of BD+43 degrees 3654 by XMM-Newton to search for the presence of non-thermal X-ray emission. We found no evidence of non-thermal emission spatially coincident with the bow shocks; nonetheless, diffuse emission was detected in the vicinity of zeta Oph. After a careful analysis of its spectral characteristics, we conclude that this emission has a thermal nature with a plasma temperature of T approximate to 2 x 10(6) K. The cometary shape of this emission seems to be in line with recent predictions of radiation-hydrodynamic models of runaway stars. The case of BD+43 degrees 3654 is puzzling, as non-thermal emission has been reported in a previous work for this source. KW - stars: individual (zeta Oph, BD+43 degrees 3654) KW - stars: winds, outflows Y1 - 2016 U6 - https://doi.org/10.3847/0004-637X/821/2/79 SN - 0004-637X SN - 1538-4357 VL - 821 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Oskinova, Lida A1 - Feldmeier, Achim A1 - Hamann, Wolf-Rainer T1 - X-ray line profiles from structured stellar winds N2 - Absorbing material compressed in a number of thin shells is effectively less opaque for X-rays than smoothly distributed gas. The calculated X-ray emission line profiles are red-shifted if the emission arises from the starward side of the shells. Y1 - 2003 SN - 1-58381-133-8 ER - TY - JOUR A1 - Feldmeier, Achim A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer T1 - X-ray line emission from a fragmented stellar wind N2 - We discuss X-ray line formation in dense O star winds. A random distribution of wind shocks is assumed to emit X-rays that are partially absorbed by cooler wind gas. The cool gas resides in highly compressed fragments oriented perpendicular to the radial flow direction. For fully opaque fragments, we find that the blueshifted part of X-ray line profiles remains flat-topped even after severe wind attenuation, whereas the red part shows a steep decline. These box- type, blueshifted profiles resemble recent Chandra observations of the O3 star zeta Pup. For partially transparent fragments, the emission lines become similar to those from a homogeneous wind. Y1 - 2003 ER - TY - JOUR A1 - Oskinova, Lida A1 - Feldmeier, Achim A1 - Hamann, Wolf-Rainer T1 - X-ray emission lines from inhomogeneous stellar winds N2 - It is commonly adopted that X-rays from O stars are produced deep inside the stellar wind, and transported outwards through the bulk of the expanding matter which attenuates the radiation and affects the shape of emission line profiles. The ability of the X-ray observatories Chandra and XMM-Newton to resolve these lines spectroscopically provided a stringent test for the theory of the X-ray production. It turned out that none of the existing models was able to fit the observations consistently. The possible caveat of these models was the underlying assumption of a smooth stellar wind. Motivated by the evidence that the stellar winds are in fact structured, we present a 2-D numerical model of a stochastic, inhomogeneous wind. Small parcels of hot, X-ray emitting gas are permeated by cool, absorbing wind material which is compressed into thin shell fragments. Wind fragmentation alters the radiative transfer drastically, compared to homogeneous models of the same mass-loss rate. X-rays produced deep inside the wind, which would be totally absorbed in a homogeneous flow, can effectively escape from a fragmented wind. The wind absorption becomes wavelength independent if the individual fragments are optically thick. The X-ray line profiles are flat-topped in the blue part and decline steeply in the red part for the winds with a short acceleration zone. For the winds where the acceleration extends over significant distances, the lines can appear nearly symmetric and only slightly blueshifted, in contrast to the skewed, triangular line profiles typically obtained from homogeneous wind models of high optical depth. We show that profiles from a fragmented wind model can reproduce the observed line profiles from zeta Orionis. The present numerical modeling confirms the results from a previous study, where we derived analytical formulae from a statistical treatment Y1 - 2004 SN - 0004-6361 ER - TY - JOUR A1 - Parkin, E. R. A1 - Broos, Patrick S. A1 - Townsley, L. K. A1 - Pittard, J. M. A1 - Moffat, Anthony F. J. A1 - Naze, Y. A1 - Rauw, G. A1 - Oskinova, Lida A1 - Waldron, W. L. T1 - X-RAY EMISSION FROM THE DOUBLE-BINARY OB-STAR SYSTEM QZ CAR (HD 93206) JF - ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES N2 - X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The respective orbits of systems A (O9.7 I+b2 v, P-A = 21 days) and B (O8 III+o9 v, P-B = 6 days) are reasonably well sampled by the observations, allowing the origin of the X-ray emission to be examined in detail. The X-ray spectra can be well fitted by an attenuated three-temperature thermal plasma model, characterized by cool, moderate, and hot plasma components at kT similar or equal to 0.2, 0.7, and 2 keV, respectively, and a circumstellar absorption of similar or equal to 0.2 x 10(22) cm(-2). Although the hot plasma component could be indicating the presence of wind-wind collision shocks in the system, the model fluxes calculated from spectral fits, with an average value of similar or equal to 7x10(-13) erg s(-1) cm(-2), do not show a clear correlation with the orbits of the two constituent binaries. A semi-analytical model of QZ Car reveals that a stable momentum balance may not be established in either system A or B. Yet, despite this, system B is expected to produce an observed X-ray flux well in excess of the observations. If one considers the wind of the O8 III star to be disrupted by mass transfer, the model and observations are in far better agreement, which lends support to the previous suggestion of mass transfer in the O8 III+o9 v binary. We conclude that the X-ray emission from QZ Car can be reasonably well accounted for by a combination of contributions mainly from the single stars and the mutual wind-wind collision between systems A and B. KW - hydrodynamics KW - stars: early-type KW - stars: individual (QZ Carinae) KW - stars: massive KW - stars: winds, outflows KW - X-rays: stars Y1 - 2011 U6 - https://doi.org/10.1088/0067-0049/194/1/8 SN - 0067-0049 VL - 194 IS - 1 PB - IOP PUBLISHING LTD CY - BRISTOL ER - TY - JOUR A1 - Oskinova, Lida T1 - X-ray emission from single WR stars JF - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015 N2 - In this review I briefly summarize our knowledge of the X-ray emission from single WN, WC, and WO stars. These stars have relatively modest X-ray luminosities, typically not exceeding 1L⊙. The analysis of X-ray spectra usually reveals thermal plasma with temperatures reaching a few x10 MK. X-ray variability is detected in some WN stars. At present we don't fully understand how X-ray radiation in produced in WR stars, albeit there are some promising research avenues, such as the presence of CIRs in the winds of some stars. To fully understand WR stars we need to unravel mechanisms of X-ray production in their winds. Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88228 SP - 295 EP - 300 ER - TY - JOUR A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Cassinelli, Joseph P. A1 - Brown, John C. A1 - Todt, Helge Tobias T1 - X-ray emission from massive stars with magnetic fields JF - Astronomische Nachrichten = Astronomical notes N2 - We investigate the connections between the magnetic fields and the X-ray emission from massive stars. Our study shows that the X-ray properties of known strongly magnetic stars are diverse: while some comply to the predictions of the magnetically confined wind model, others do not. We conclude that strong, hard, and variable X-ray emission may be a sufficient attribute of magnetic massive stars, but it is not a necessary one. We address the general properties of X-ray emission from "normal" massive stars, especially the long standing mystery about the correlations between the parameters of X-ray emission and fundamental stellar properties. The recent development in stellar structure modeling shows that small-scale surface magnetic fields may be common. We suggest a "hybrid" scenario which could explain the X-ray emission from massive stars by a combination of magnetic mechanisms on the surface and shocks in the stellar wind. The magnetic mechanisms and the wind shocks are triggered by convective motions in sub-photospheric layers. This scenario opens the door for a natural explanation of the well established correlation between bolometric and X-ray luminosities. KW - stars: magnetic fields KW - stars: mass-loss KW - stars: winds, outflows KW - stars: Wolf-Rayet KW - techniques: spectroscopic KW - X-rays: stars Y1 - 2011 U6 - https://doi.org/10.1002/asna.201111602 SN - 0004-6337 VL - 332 IS - 9-10 SP - 988 EP - 993 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Oskinova, Lida T1 - X-ray diagnostics of massive star winds JF - Advances in space research N2 - Nearly all types of massive stars with radiatively driven stellar winds are X-ray sources that can be observed by the presently operating powerful X-ray telescopes. In this review I briefly address recent advances in our understanding of stellar winds obtained from X-ray observations. X-rays may strongly influence the dynamics of weak winds of main sequence B-type stars. X-ray pulsations were detected in a beta Cep type variable giving evidence of tight photosphere-wind connections. The winds of OB dwarfs with subtypes later than O9V may be predominantly in a hot phase, and X-ray observations offer the best window for their studies. The X-ray properties of OB super giants are largely determined by the effects of radiative transfer in their clumped stellar winds. The recently suggested method to directly measure mass-loss rates of O stars by fitting the shapes of X-ray emission lines is considered but its validity cannot be confirmed. To obtain robust quantitative information on stellar wind parameters from X-ray spectroscopy, a multiwavelength analysis by means of stellar atmosphere models is required. Independent groups are now performing such analyses with encouraging results. Joint analyses of optical, UV, and X-ray spectra of OB supergiants yield consistent mass-loss rates. Depending on the adopted clumping parameters, the empirically derived mass-loss rates are a factor of a few smaller or comparable to those predicted by standard recipes (Vink et al., 2001). All sufficiently studied O stars display variable X-ray emission that might be related to corotating interaction regions in their winds. In the latest stages of stellar evolution, single red supergiants (RSG) and luminous blue variable (LBV) stars do not emit observable amounts of X-rays. On the other hand, nearly all types of Wolf-Rayet (WR) stars are X-ray sources. X-ray spectroscopy allows a sensitive probe of WR wind abundances and opacities. (C) 2016 COSPAR. Published by Elsevier Ltd. All rights reserved. KW - Blue stars KW - Stellar winds KW - X-ray emission spectra Y1 - 2016 U6 - https://doi.org/10.1016/j.asr.2016.06.030 SN - 0273-1177 SN - 1879-1948 VL - 58 SP - 739 EP - 760 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Shenar, Tomer A1 - Hainich, Rainer A1 - Todt, Helge Tobias A1 - Sander, Andreas Alexander Christoph A1 - Hamann, Wolf-Rainer A1 - Moffat, Anthony F. J. A1 - Eldridge, J. J. A1 - Pablo, H. A1 - Oskinova, Lida A1 - Richardson, N. D. T1 - Wolf-Rayet stars in the Small Magellanic Cloud II. Analysis of the binaries JF - American mineralogist : an international journal of earth and planetary materials N2 - Context. Massive Wolf-Rayet (WR) stars are evolved massive stars (M-i greater than or similar to 20 M-circle dot) characterized by strong mass-loss. Hypothetically, they can form either as single stars or as mass donors in close binaries. About 40% of all known WR stars are confirmed binaries, raising the question as to the impact of binarity on the WR population. Studying WR binaries is crucial in this context, and furthermore enable one to reliably derive the elusive masses of their components, making them indispensable for the study of massive stars. Aims. By performing a spectral analysis of all multiple WR systems in the Small Magellanic Cloud (SMC), we obtain the full set of stellar parameters for each individual component. Mass-luminosity relations are tested, and the importance of the binary evolution channel is assessed. Methods. The spectral analysis is performed with the PotsdamWolf-Rayet (PoWR) model atmosphere code by superimposing model spectra that correspond to each component. Evolutionary channels are constrained using the Binary Population and Spectral Synthesis (BPASS) evolution tool. Results. Significant hydrogen mass fractions (0.1 < X-H < 0.4) are detected in all WN components. A comparison with mass-luminosity relations and evolutionary tracks implies that the majority of the WR stars in our sample are not chemically homogeneous. The WR component in the binary AB6 is found to be very luminous (log L approximate to 6.3 [L-circle dot]) given its orbital mass (approximate to 10 M-circle dot), presumably because of observational contamination by a third component. Evolutionary paths derived for our objects suggest that Roche lobe overflow had occurred in most systems, affecting their evolution. However, the implied initial masses (greater than or similar to 60 M-circle dot) are large enough for the primaries to have entered the WR phase, regardless of binary interaction. Conclusions. Together with the results for the putatively single SMC WR stars, our study suggests that the binary evolution channel does not dominate the formation of WR stars at SMC metallicity. KW - stars: massive KW - stars: Wolf-Rayet KW - stars: evolution KW - binaries: close KW - binaries: symbiotic KW - Magellanic Clouds Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527916 SN - 1432-0746 VL - 591 PB - EDP Sciences CY - Les Ulis ER - TY - GEN A1 - Todt, Helge Tobias A1 - Peña, Miriam A1 - Zühlke, Julia A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Gräfener, Götz T1 - Weak emission line central stars of planetary nebulae T2 - Planetary Nebulae: an Eye to the Future N2 - To understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 462 KW - stars: AGB and post-AGB KW - stars: Wolf-Rayet KW - stars: abundances Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413775 ER - TY - GEN A1 - Vink, Jorick Sandor A1 - Heger, Alexander A1 - Krumholz, Mark R. A1 - Puls, Joachim A1 - Banerjee, Shiladitya A1 - Castro, Norberto A1 - Chen, K.-J. A1 - Chenè, A.-N. A1 - Crowther, P. A. A1 - Daminelli, A. A1 - Gräfener, G. A1 - Groh, J. H. A1 - Hamann, Wolf-Rainer A1 - Heap, S. A1 - Herrero, A. A1 - Kaper, L. A1 - Najarro, F. A1 - Oskinova, Lida A1 - Roman-Lopes, A. A1 - Rosen, A. A1 - Sander, A. A1 - Shirazi, M. A1 - Sugawara, Y. A1 - Tramper, F. A1 - Vanbeveren, D. A1 - Voss, R. A1 - Wofford, A. A1 - Zhang, Y. T1 - Very massive stars in the local universe T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Recent studies have claimed the existence of very massive stars (VMS) up to 300 M⊙ in the local Universe. As this finding may represent a paradigm shift for the canonical stellar upper-mass limit of 150 M⊙, it is timely to discuss the status of the data, as well as the far-reaching implications of such objects. We held a Joint Discussion at the General Assembly in Beijing to discuss (i) the determination of the current masses of the most massive stars, (ii) the formation of VMS, (iii) their mass loss, and (iv) their evolution and final fate. The prime aim was to reach broad consensus between observers and theorists on how to identify and quantify the dominant physical processes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 601 KW - stars: massive stars KW - stars: mass-loss KW - stars: stellar evolution Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-415220 SN - 1866-8372 IS - 601 ER - TY - JOUR A1 - Oskinova, Lida A1 - Bik, A. A1 - Mas-Hesse, J. M. A1 - Hayes, M. A1 - Adamo, A. A1 - Östlin, Göran A1 - Fürst, F. A1 - Otí-Floranes, H. T1 - ULX contribution to stellar feedback BT - an intermediate-mass black hole candidate and the population of ULXs in the low-metallicity starburst galaxy ESO338-4 JF - Astronomy and astrophysics : an international weekly journal N2 - Context. X-ray radiation from accreting compact objects is an important part of stellar feedback. The metal-poor galaxy ESO 338-4 has experienced vigorous starburst during the last <40 Myr and contains some of the most massive super star clusters in the nearby Universe. Given its starburst age and its star-formation rate, ESO 338-4 is one of the most efficient nearby manufactures of neutron stars and black holes, hence providing an excellent laboratory for feedback studies. Aims. We aim to use X-ray observations with the largest modern X-ray telescopes XMM-Newton and Chandra to unveil the most luminous accreting neutron stars and black holes in ESO 338-4. Methods. We compared X-ray images and spectra with integral field spectroscopic observations in the optical to constrain the nature of strong X-ray emitters. Results. X-ray observations uncover three ultraluminous X-ray sources (ULXs) in ESO 338-4. The brightest among them, ESO 338 X-1, has X-ray luminosity in excess of 10(40) erg s(-1). We speculate that ESO 338-4 X-1 is powered by accretion on an intermediate-mass (greater than or similar to 300 M-circle dot)black hole. We show that X-ray radiation from ULXs and hot superbubbles strongly contributes to He II ionization and general stellar feedback in this template starburst galaxy. KW - galaxies: dwarf KW - galaxies: individual: ESO 338-4 KW - X-rays: binaries KW - X-rays: ISM Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201935414 SN - 1432-0746 VL - 627 PB - EDP Sciences CY - Les Ulis ER - TY - GEN A1 - Barniske, Andreas A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer T1 - Two extremely luminous WN stars in the Galactic center with circumstellar emission from dust and gas (vol 486, pg 971, 2008) T2 - Physical chemistry, chemical physics : a journal of European Chemical Societies KW - stars: Wolf-Rayet KW - HII regions KW - Galaxy: center KW - stars: individual: WR 102ka KW - stars: individual: WR 102c KW - errata, addenda Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/200809568e SN - 1432-0746 VL - 587 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Martinez-Nunez, Silvia A1 - Kretschmar, Peter A1 - Bozzo, Enrico A1 - Oskinova, Lida A1 - Puls, Joachim A1 - Sidoli, Lara A1 - Sundqvist, Jon Olof A1 - Blay, Pere A1 - Falanga, Maurizio A1 - Furst, Felix A1 - Gimenez-Garcia, Angel A1 - Kreykenbohm, Ingo A1 - Kuehnel, Matthias A1 - Sander, Andreas Alexander Christoph A1 - Torrejon, Jose Miguel A1 - Wilms, Joern T1 - Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries JF - Space science reviews N2 - Massive stars, at least similar to 10 times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy. In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense "clumps". The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution. Supergiant high mass X-ray binaries (SgXBs) are among the brightest X-ray sources in the sky. A large number of them consist of a neutron star accreting from the wind of a massive companion and producing a powerful X-ray source. The characteristics of the stellar wind together with the complex interactions between the compact object and the donor star determine the observed X-ray output from all these systems. Consequently, the use of SgXBs for studies of massive stars is only possible when the physics of the stellar winds, the compact objects, and accretion mechanisms are combined together and confronted with observations. This detailed review summarises the current knowledge on the theory and observations of winds from massive stars, as well as on observations and accretion processes in wind-fed high mass X-ray binaries. The aim is to combine in the near future all available theoretical diagnostics and observational measurements to achieve a unified picture of massive star winds in isolated objects and in binary systems. KW - Massive stars KW - Stellar outflows KW - X-ray binary KW - Wind-fed systems KW - Accretion processes KW - SgXBs KW - SFXTs Y1 - 2017 U6 - https://doi.org/10.1007/s11214-017-0340-1 SN - 0038-6308 SN - 1572-9672 VL - 212 SP - 59 EP - 150 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Surlan, B. A1 - Hamann, Wolf-Rainer A1 - Kubat, Jirij A1 - Oskinova, Lida A1 - Feldmeier, Achim T1 - Three-dimensional radiative transfer in clumped hot star winds I influence of clumping on the resonance line formation JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The true mass-loss rates from massive stars are important for many branches of astrophysics. For the correct modeling of the resonance lines, which are among the key diagnostics of stellar mass-loss, the stellar wind clumping has been found to be very important. To incorporate clumping into a radiative transfer calculation, three-dimensional (3D) models are required. Various properties of the clumps may have a strong impact on the resonance line formation and, therefore, on the determination of empirical mass-loss rates. Aims. We incorporate the 3D nature of the stellar wind clumping into radiative transfer calculations and investigate how different model parameters influence the resonance line formation. Methods. We develop a full 3D Monte Carlo radiative transfer code for inhomogeneous expanding stellar winds. The number density of clumps follows the mass conservation. For the first time, we use realistic 3D models that describe the dense as well as the tenuous wind components to model the formation of resonance lines in a clumped stellar wind. At the same time, we account for non-monotonic velocity fields. Results. The 3D density and velocity wind inhomogeneities show that there is a very strong impact on the resonance line formation. The different parameters describing the clumping and the velocity field results in different line strengths and profiles. We present a set of representative models for various sets of model parameters and investigate how the resonance lines are affected. Our 3D models show that the line opacity is lower for a larger clump separation and shallower velocity gradients within the clumps. Conclusions. Our model demonstrates that to obtain empirically correct mass-loss rates from the UV resonance lines, the wind clumping and its 3D nature must be taken into account. KW - stars: winds, outflows KW - stars: mass-loss KW - stars: early-type Y1 - 2012 U6 - https://doi.org/10.1051/0004-6361/201118590 SN - 0004-6361 VL - 541 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Ignace, Rico A1 - Gayley, Kenneth G. A1 - Hamann, Wolf-Rainer A1 - Huenemoerder, David P. A1 - Oskinova, Lida A1 - Pollock, Andy M. T. A1 - McFall, Michael T1 - THE XMM-NEWTON/EPIC X-RAY LIGHT CURVE ANALYSIS OF WR 6 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We obtained four pointings of over 100 ks each of the well-studied Wolf-Rayet star WR 6 with the XMM-Newton satellite. With a first paper emphasizing the results of spectral analysis, this follow-up highlights the X-ray variability clearly detected in all four pointings. However, phased light curves fail to confirm obvious cyclic behavior on the well-established 3.766 day period widely found at longer wavelengths. The data are of such quality that we were able to conduct a search for event clustering in the arrival times of X-ray photons. However, we fail to detect any such clustering. One possibility is that X-rays are generated in a stationary shock structure. In this context we favor a corotating interaction region (CIR) and present a phenomenological model for X-rays from a CIR structure. We show that a CIR has the potential to account simultaneously for the X-ray variability and constraints provided by the spectral analysis. Ultimately, the viability of the CIR model will require both intermittent long-term X-ray monitoring of WR 6 and better physical models of CIR X-ray production at large radii in stellar winds. KW - stars: individual (WR 6) KW - stars: winds, outflows KW - stars: Wolf-Rayet KW - X-rays: stars Y1 - 2013 U6 - https://doi.org/10.1088/0004-637X/775/1/29 SN - 0004-637X VL - 775 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Gomez-Moran, Ada Nebot A1 - Oskinova, Lida T1 - The X-ray catalog of spectroscopically identified Galactic O stars Investigating the dependence of X-ray luminosity on stellar and wind parameters JF - Astronomy and astrophysics : an international weekly journal N2 - The X-ray emission of O-type stars was first discovered in the early days of the Einstein satellite. Since then many different surveys have confirmed that the ratio of X-ray to bolometric luminosity in O-type stars is roughly constant, but there is a paucity of studies that account for detailed information on spectral and wind properties of O-stars. Recently a significant sample of O stars within our Galaxy was spectroscopically identified and presented in the Galactic O-Star Spectroscopic Survey (GOSS). At the same time, a large high-fidelity catalog of X-ray sources detected by the XMM-Newton X-ray telescope was released. Here we present the X-ray catalog of O stars with known spectral types and investigate the dependence of their X-ray properties on spectral type as well as stellar and wind parameters. We find that, among the GOSS sample, 127 O-stars have a unique XMM-Newton source counterpart and a Gaia data release 2 (DR2) association. Terminal velocities are known for a subsample of 35 of these stars. We confirm that the X-ray luminosities of dwarf and giant O stars correlate with their bolometric luminosity. For the subsample of O stars with measure terminal velocities we find that the X-ray luminosities of dwarf and giant O stars also correlate with wind parameters. However, we find that these correlations break down for supergiant stars. Moreover, we show that supergiant stars are systematically harder in X-rays compared to giant and dwarf O-type stars. We find that the X-ray luminosity depends on spectral type, but seems to be independent of whether the stars are single or in a binary system. Finally, we show that the distribution of log(L-X/L-bol) in our sample stars is non-Gaussian, with the peak of the distribution at log(L-X/L-bol) approximate to -6.6. KW - stars: massive KW - X-rays: stars Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201833453 SN - 1432-0746 VL - 620 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Steinke, M. A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Sander, A. T1 - The Wolf-Rayet stars WR102c and 102ka and their isolation JF - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015 N2 - While the majority of very massive stars is clearly found in clusters, there are also very massive objects not associated with any cluster, suggesting they may have been born in isolation. In order to gain more insights, we studied the regions around two WR stars in the Galactic Center region. To understand the nature of the potential cluster around massive stars, photometry alone is not sufficient. We therefore used the ESO VLT/SINFONI integral field spectrograph to obtain photometry and spectra for the whole region around our two candidate stars. In total, more than 60 stars have been found and assigned a spectral type. Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88503 SP - 365 ER - TY - JOUR A1 - Hainich, Rainer A1 - Ruehling, Ute A1 - Todt, Helge Tobias A1 - Oskinova, Lida A1 - Liermann, A. A1 - Graefener, G. A1 - Foellmi, C. A1 - Schnurr, O. A1 - Hamann, Wolf-Rainer T1 - The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Massive stars, although being important building blocks of galaxies, are still not fully understood. This especially holds true for Wolf-Rayet (WR) stars with their strong mass loss, whose spectral analysis requires adequate model atmospheres. Aims. Following our comprehensive studies of the WR stars in the Milky Way, we now present spectroscopic analyses of almost all known WN stars in the LMC. Methods. For the quantitative analysis of the wind-dominated emission-line spectra, we employ the Potsdam Wolf-Rayet (PoWR) model atmosphere code. By fitting synthetic spectra to the observed spectral energy distribution and the available spectra (ultraviolet and optical), we obtain the physical properties of 107 stars. Results. We present the fundamental stellar and wind parameters for an almost complete sample of WN stars in the LMC. Among those stars that are putatively single, two different groups can be clearly distinguished. While 12% of our sample are more luminous than 10(6) L-circle dot and contain a significant amount of hydrogen, 88% of the WN stars, with little or no hydrogen, populate the luminosity range between log (L/L-circle dot) = 5.3 ... 5.8. Conclusions. While the few extremely luminous stars (log (L/L-circle dot) > 6), if indeed single stars, descended directly from the main sequence at very high initial masses, the bulk of WN stars have gone through the red-supergiant phase. According to their luminosities in the range of log (L/L-circle dot) = 5.3 ... 5.8, these stars originate from initial masses between 20 and 40 M-circle dot. This mass range is similar to the one found in the Galaxy, i.e. the expected metallicity dependence of the evolution is not seen. Current stellar evolution tracks, even when accounting for rotationally induced mixing, still partly fail to reproduce the observed ranges of luminosities and initial masses. Moreover, stellar radii are generally larger and effective temperatures correspondingly lower than predicted from stellar evolution models, probably due to subphotospheric inflation. KW - stars: Wolf-Rayet KW - Magellanic Clouds KW - stars: early-type KW - stars: atmospheres KW - stars: winds, outflows KW - stars: mass-loss Y1 - 2014 U6 - https://doi.org/10.1051/0004-6361/201322696 SN - 0004-6361 SN - 1432-0746 VL - 565 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Shenar, Tomer A1 - Sablowski, D. P. A1 - Hainich, Rainer A1 - Todt, Helge Tobias A1 - Moffat, Anthony F. J. A1 - Oskinova, Lida A1 - Ramachandran, Varsha A1 - Sana, Hugues A1 - Sander, Andreas Alexander Christoph A1 - Schnurr, O. A1 - St-Louis, N. A1 - Vanbeveren, D. A1 - Gotberg, Y. A1 - Hamann, Wolf-Rainer T1 - The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud Spectroscopy, orbital analysis, formation, and evolution JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Massive Wolf-Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z approximate to 0.5 Z(circle dot)), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf-Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45 +/- 30% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only approximate to 12 +/- 7% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises approximate to 4% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L approximate to 5.2 [L-circle dot], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (v(eq) less than or similar to 250 km s(-1)) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models. KW - stars: massive KW - stars: Wolf-Rayet KW - Magellanic Clouds KW - binaries: close KW - binaries: spectroscopic KW - stars: evolution Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201935684 SN - 0004-6361 SN - 1432-0746 VL - 627 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Shenar, Tomer A1 - Richardson, N. D. A1 - Sablowski, Daniel P. A1 - Hainich, Rainer A1 - Sana, H. A1 - Moffat, A. F. J. A1 - Todt, Helge Tobias A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Sander, Andreas Alexander Christoph A1 - Tramper, Frank A1 - Langer, Norbert A1 - Bonanos, Alceste Z. A1 - de Mink, Selma E. A1 - Gräfener, G. A1 - Crowther, Paul A1 - Vink, J. S. A1 - Almeida, Leonardo A. A1 - de Koter, A. A1 - Barbá, Rodolfo A1 - Herrero, A. A1 - Ulaczyk, Krzysztof T1 - The tarantula massive binary monitoring BT - II. First SB2 orbital and spectroscopic analysis for the Wolf-Rayet binary R145 JF - Astronomy and astrophysics : an international weekly journal N2 - We present the first SB2 orbital solution and disentanglement of the massive Wolf-Rayet binary R145 (P = 159 d) located in the Large Magellanic Cloud. The primary was claimed to have a stellar mass greater than 300 M-circle dot, making it a candidate for being the most massive star known to date. While the primary is a known late-type, H-rich Wolf-Rayet star (WN6h), the secondary has so far not been unambiguously detected. Using moderate-resolution spectra, we are able to derive accurate radial velocities for both components. By performing simultaneous orbital and polarimetric analyses, we derive the complete set of orbital parameters, including the inclination. The spectra are disentangled and spectroscopically analyzed, and an analysis of the wind-wind collision zone is conducted. The disentangled spectra and our models are consistent with a WN6h type for the primary and suggest that the secondary is an O3.5 If*/WN7 type star. We derive a high eccentricity of e = 0 : 78 and minimum masses of M-1 sin(3) i approximate to M-2 sin(3) i = 13 +/- 2 M-circle dot, with q = M-2/M-1 = 1.01 +/- 0.07. An analysis of emission excess stemming from a wind-wind collision yields an inclination similar to that obtained from polarimetry (i = 39 +/- 6 degrees). Our analysis thus implies M-1 = 53(-20)(+40) and M2 = 54(-20)(+40) M-circle dot, excluding M-1 > 300 M-circle dot. A detailed comparison with evolution tracks calculated for single and binary stars together with the high eccentricity suggests that the components of the system underwent quasi-homogeneous evolution and avoided mass-transfer. This scenario would suggest current masses of approximate to 80 M-circle dot and initial masses of M-i,M-1 approximate to 10(5) and M-i,M-2 approximate to 90 M-circle dot, consistent with the upper limits of our derived orbital masses, and would imply an age of approximate to 2.2 Myr. KW - binaries: spectroscopic KW - stars: Wolf-Rayet KW - stars: massive KW - Magellanic Clouds KW - stars: individual: R 145 KW - stars: atmospheres Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201629621 SN - 1432-0746 VL - 598 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Bozzo, Enrico A1 - Romano, Patrizia A1 - Ferrigno, Carlo A1 - Oskinova, Lida T1 - The symbiotic X-ray binaries Sct X-1, 4U 1700+24, and IGR J17329-2731 JF - Monthly notices of the Royal Astronomical Society N2 - Symbiotic X-ray binaries are systems hosting a neutron star accreting form the wind of a late-type companion. These are rare objects and so far only a handful of them are known. One of the most puzzling aspects of the symbiotic X-ray binaries is the possibility that they contain strongly magnetized neutron stars. These are expected to be evolutionary much younger compared to their evolved companions and could thus be formed through the (yet poorly known) accretion induced collapse of a white dwarf. In this paper, we perform a broad-band X-ray and soft gamma-ray spectroscopy of two known symbiotic binaries, Sct X-1 and 4U 1700+24, looking for the presence of cyclotron scattering features that could confirm the presence of strongly magnetized NSs. We exploited available Chandra, Swift, and NuSTAR data. We find no evidence of cyclotron resonant scattering features (CRSFs) in the case of Sct X-1 but in the case of 4U 1700+24 we suggest the presence of a possible CRSF at similar to 16 keV and its first harmonic at similar to 31 keV, although we could not exclude alternative spectral models for the broad-band fit. If confirmed by future observations, 4U 1700+24 could be the second symbiotic X-ray binary with a highly magnetized accretor. We also report about our long-term monitoring of the last discovered symbiotic X-ray binary IGR J17329-2731 performed with Swift/XRT. The monitoring revealed that, as predicted, in 2017 this object became a persistent and variable source, showing X-ray flares lasting for a few days and intriguing obscuration events that are interpreted in the context of clumpy wind accretion. KW - accretion KW - accretion discs KW - stars: massive KW - stars: neutron KW - X-rays: binaries KW - X-rays: individual: SctX-1 KW - X-rays: individual: 4U1700+24; KW - X-rays: stars KW - X-rays: individual: IGRJ17329-2731 Y1 - 2022 U6 - https://doi.org/10.1093/mnras/stac907 SN - 0035-8711 SN - 1365-2966 VL - 513 IS - 1 SP - 42 EP - 54 PB - Oxford University Press CY - Oxford ER - TY - JOUR A1 - Bozzo, Enrico A1 - Oskinova, Lida A1 - Lobel, A. A1 - Hamann, Wolf-Rainer T1 - The super-orbital modulation of supergiant high-mass X-ray binaries JF - Astronomy and astrophysics : an international weekly journal N2 - The long-term X-ray light curves of classical supergiant X-ray binaries and supergiant fast X-ray transients show relatively similar super-orbital modulations, which are still lacking a sound interpretation. We propose that these modulations are related to the presence of corotating interaction regions (CIRs) known to thread the winds of OB supergiants. To test this hypothesis, we couple the outcomes of three-dimensional (3D) hydrodynamic models for the formation of CIRs in stellar winds with a simplified recipe for the accretion onto a neutron star. The results show that the synthetic X-ray light curves are indeed modulated by the presence of the CIRs. The exact period and amplitude of these modulations depend on a number of parameters governing the hydrodynamic wind models and on the binary orbital configuration. To compare our model predictions with the observations, we apply the 3D wind structure previously shown to well explain the appearance of discrete absorption components in the UV time series of a prototypical B0.5I-type supergiant. Using the orbital parameters of IGRJ 16493-4348, which has the same B0.5I donor spectral type, the period and modulations in the simulated X-ray light curve are similar to the observed ones, thus providing support to our scenario. We propose that the presence of CIRs in donor star winds should be considered in future theoretical and simulation efforts of wind-fed X-ray binaries. KW - X-rays: stars KW - X-rays: binaries KW - gamma rays: stars KW - stars: massive KW - stars: neutron Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201731930 SN - 1432-0746 VL - 606 PB - EDP Sciences CY - Les Ulis ER - TY - GEN A1 - Oskinova, Lida A1 - Guerrero, Martín A. A1 - Hénault-Brunet, Vincent A1 - Sun, W. A1 - Chu, You-Hua A1 - Evans, Chris A1 - Gallagher, John S. A1 - Gruendl, Robert A. A1 - Reyes-Iturbide, Jorge T1 - The slow X-ray pulsar SXP 1062 and associated supernova remnant in the Wing of the Small Magellanic Cloud T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - SXP 1062 is an exceptional case of a young neutron star in a wind-fed high-mass X-ray binary associated with a supernova remnant. A unique combination of measured spin period, its derivative, luminosity and young age makes this source a key probe for the physics of accretion and neutron star evolution. Theoretical models proposed to explain the properties of SXP 1062 shall be tested with new data. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 591 KW - stars: emission-line KW - Be KW - X-rays: binaries KW - pulsars: individual (SXP 1062) Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-415135 SN - 1866-8372 IS - 591 ER - TY - JOUR A1 - Shenar, Tomer A1 - Hainich, Rainer A1 - Todt, Helge Tobias A1 - Moffat, Anthony F. J. A1 - Sander, Andreas Alexander Christoph A1 - Oskinova, Lida A1 - Ramachandran, Varsha A1 - Munoz, M. A1 - Pablo, H. A1 - Sana, Hugues A1 - Hamann, Wolf-Rainer T1 - The shortest-period Wolf-Rayet binary in the small magellanic cloud BT - Part of a high-order multiple system Spectral and orbital analysis of SMC AB 6 JF - Astronomy and astrophysics : an international weekly journal N2 - Context. SMC AB6 is the shortest-period (P = 6.5 d) Wolf-Rayet (WR) binary in the Small Magellanic Cloud. This binary is therefore a key system in the study of binary interaction and formation of WR stars at low metallicity. The WR component in AB6 was previously found to be very luminous (log L = 6.3 [L-circle dot]) compared to its reported orbital mass (approximate to 8 M-circle dot), placing it significantly above the Eddington limit. Aims. Through spectroscopy and orbital analysis of newly acquired optical data taken with the Ultraviolet and Visual Echelle Spectrograph (UVES), we aim to understand the peculiar results reported for this system and explore its evolutionary history. Methods. We measured radial velocities via cross-correlation and performed a spectral analysis using the Potsdam Wolf-Rayet model atmosphere code. The evolution of the system was analyzed using the Binary Population and Spectral Synthesis evolution code. Results. AB6 contains at least four stars. The 6.5 d period WR binary comprises the WR primary (WN3:h, star A) and a rather rapidly rotating (v(eq) = 265 km s(-1)) early O-type companion (O5.5 V, star B). Static N III and N IV emission lines and absorption signatures in He lines suggest the presence of an early-type emission line star (O5.5 I(f), star C). Finally, narrow absorption lines portraying a long-term radial velocity variation show the existence of a fourth star (O7.5 V, star D). Star D appears to form a second 140 d period binary together with a fifth stellar member, which is a B-type dwarf or a black hole. It is not clear that these additional components are bound to the WR binary. We derive a mass ratio of M-O/M-WR = 2.2 +/- 0.1. The WR star is found to be less luminous than previously thought (log L = 5.9 [L-circle dot]) and, adopting M-O = 41 M-circle dot for star B, more massive (M-WR = 18 M-circle dot). Correspondingly, the WR star does not exceed the Eddington limit. We derive the initial masses of M-i,M-WR = 60 M-circle dot and M-i,M-O = 40 M-circle dot and an age of 3.9 Myr for the system. The WR binary likely experienced nonconservative mass transfer in the past supported by the relatively rapid rotation of star B. Conclusions. Our study shows that AB6 is a multiple - probably quintuple - system. This finding resolves the previously reported puzzle of the WR primary exceeding the Eddington limit and suggests that the WR star exchanged mass with its companion in the past. KW - stars: massive KW - binaries: spectroscopic KW - stars: Wolf-Rayet KW - Magellanic Clouds KW - stars: individual: SMC AB 6 KW - stars: atmospheres Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201833006 SN - 1432-0746 SN - 0004-6361 VL - 616 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Evans, Nancy Remage A1 - DeGioia-Eastwood, Kathleen A1 - Gagne, Marc A1 - Townsley, Leisa A1 - Broos, Patrick S. A1 - Wolk, Scott J. A1 - Naze, Yael A1 - Corcoran, Michael A1 - Oskinova, Lida A1 - Moffat, Anthony F. J. A1 - Wang, Junfeng A1 - Walborn, Nolan R. T1 - The search for low-mass companions of b stars in the Carina Nebula cluster trumpler 16 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series N2 - We have developed lists of likely B3-A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of eta Car, an appropriate V and B - V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B - V) = 0.55 mag +/- 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project. Previous studies have shown that only very rarely (if at all) do late main-sequence B stars produce X-rays. We present evidence that the X-ray-detected sources are binaries with low-mass companions, since stars less massive than 1.4 M-circle dot are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate-mass stars are complementary to spectroscopic and interferometric results and probe new parameter space of low-mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 M-circle dot) primaries, such as would be found by random pairing from the initial mass function. KW - open clusters and associations: individual (Trumpler 16) KW - stars: massive Y1 - 2011 U6 - https://doi.org/10.1088/0067-0049/194/1/13 SN - 0067-0049 VL - 194 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Liermann, Angelika A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida T1 - The quintuplet cluster III. Hertzsprung-Russell diagram and cluster age (vol 540, pg A14, 2012) T2 - Astronomy and astrophysics : an international weekly journal KW - open clusters and associations: individual: Quintuplet KW - infrared: stars KW - stars: early-type KW - stars: late-type KW - Hertzsprung-Russell and C-M diagrams KW - errata, addenda Y1 - 2014 U6 - https://doi.org/10.1051/0004-6361/201117534e SN - 0004-6361 SN - 1432-0746 VL - 563 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Liermann, A. A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida T1 - The Quintuplet cluster III. Hertzsprung-Russell diagram and cluster age JF - Astronomy and astrophysics : an international weekly journal N2 - The Quintuplet, one of three massive stellar clusters in the Galactic center (GC), is located about 30 pc in projection from Sagittarius A*. We aim at the construction of the Hertzsprung-Russell diagram (HRD) of the cluster to study its evolution and to constrain its star-formation history. For this purpose we use the most complete spectral catalog of the Quintuplet stars. Based on the K-band spectra we determine stellar temperatures and luminosities for all stars in the catalog under the assumption of a uniform reddening towards the cluster. We find two groups in the resulting HRD: early-type OB stars and late-type KM stars, well separated from each other. By comparison with Geneva stellar evolution models we derive initial masses exceeding 8 M-circle dot for the OB stars. In the HRD these stars are located along an isochrone corresponding to an age of about 4 Myr. This confirms previous considerations, where a similar age estimate was based on the presence of evolved Wolf-Rayet stars in the cluster. We derive number ratios for the various spectral subtype groups (e.g. N-WR/N-O, N-WC/N-WN) and compare them with predictions of population synthesis models. We find that an instantaneous burst of star formation at about 3.3 to 3.6 Myr ago is the most likely scenario to form the Quintuplet cluster. Furthermore, we apply a mass-luminosity relation to construct the initial mass function (IMF) of the cluster. We find indications for a slightly top-heavy IMF. The late-type stars in the LHO catalog are red giant branch (RGB) stars or red supergiants (RSGs) according to their spectral signatures. Under the assumption that they are located at about the distance of the Galactic center we can derive their luminosities. The comparison with stellar evolution models reveals that the initial masses of these stars are lower than 15 M-circle dot implying that they needed about 15 Myr (RSG) or even more than 30 Myr (RGB) to evolve into their present stage. It might be suspected that these late-type stars do not physically belong to the Quintuplet cluster. Indeed, most of them disqualify as cluster members because their radial velocities differ too much from the cluster average. Nevertheless, five of the brightest RGB/RSG stars from the LHO catalog share the mean radial velocity of the Quintuplet, and thus remain highly suspect for being gravitationally bound members. If so, this would challenge the cluster formation and evolution scenario. KW - stars: late-type KW - Hertzsprung-Russell and C-M diagrams KW - infrared: stars KW - stars: early-type KW - open cluster and associations: individual: Quintuplet Y1 - 2012 U6 - https://doi.org/10.1051/0004-6361/201117534 SN - 0004-6361 VL - 540 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Leto, Paolo A1 - Trigilio, C. A1 - Oskinova, Lida A1 - Ignace, R. A1 - Buemi, C. S. A1 - Umana, G. A1 - Cavallaro, Francesco A1 - Ingallinera, A. A1 - Bufano, F. A1 - Phillips, N. M. A1 - Agliozzo, Claudia A1 - Cerrigone, L. A1 - Todt, Helge Tobias A1 - Riggi, S. A1 - Leone, Francesco T1 - The polarization mode of the auroral radio emission from the early-type star HD 142301 JF - Monthly notices of the Royal Astronomical Society N2 - We report the detection of the auroral radio emission from the early-type magnetic star HD142301. New VLA observations of HD142301 detected highly polarized amplified emission occurring at fixed stellar orientations. The coherent emission mechanism responsible for the stellar auroral radio emission amplifies the radiation within a narrow beam, making the star where this phenomenon occurs similar to a radio lighthouse. The elementary emission process responsible for the auroral radiation mainly amplifies one of the two magneto-ionic modes of the electromagnetic wave. This explains why the auroral pulses are highly circularly polarized. The auroral radio emission of HD142301 is characterized by a reversal of the sense of polarization as the star rotates. The effective magnetic field curve of HD142301 is also available making it possible to correlate the transition from the left to the right-hand circular polarization sense ( and vice versa) of the auroral pulses with the known orientation of the stellar magnetic field. The results presented in this letter have implications for the estimation of the dominant magneto-ionic mode amplified within the HD142301 magnetosphere. KW - masers KW - polarization KW - stars: early-type KW - stars: individual: HD142301 KW - stars: magnetic field KW - radio continuum: stars Y1 - 2018 U6 - https://doi.org/10.1093/mnrasl/sly179 SN - 0035-8711 SN - 1365-2966 VL - 482 IS - 1 SP - L4 EP - L8 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Hamann, Wolf-Rainer A1 - Gräfener, G. A1 - Liermann, A. A1 - Hainich, Rainer A1 - Sander, Andreas Alexander Christoph A1 - Shenar, Tomer A1 - Ramachandran, Varsha A1 - Todt, Helge Tobias A1 - Oskinova, Lida T1 - The Galactic WN stars revisited BT - Impact of Gaia distances on fundamental stellar parameters JF - Astronomy and astrophysics : an international weekly journal N2 - Comprehensive spectral analyses of the Galactic Wolf-Rayet stars of the nitrogen sequence (i.e. the WN subclass) have been performed in a previous paper. However, the distances of these objects were poorly known. Distances have a direct impact on the "absolute" parameters, such as luminosities and mass-loss rates. The recent Gaia Data Release (DR2) of trigonometric parallaxes includes nearly all WN stars of our Galactic sample. In the present paper, we apply the new distances to the previously analyzed Galactic WN stars and rescale the results accordingly. On this basis, we present a revised catalog of 55 Galactic WN stars with their stellar and wind parameters. The correlations between mass-loss rate and luminosity show a large scatter, for the hydrogen-free WN stars as well as for those with detectable hydrogen. The slopes of the log L - log M correlations are shallower than found previously. The empirical Hertzsprung-Russell diagram (HRD) still shows the previously established dichotomy between the hydrogen-free early WN subtypes that are located on the hot side of the zero-age main sequence (ZAMS), and the late WN subtypes, which show hydrogen and reside mostly at cooler temperatures than the ZAMS (with few exceptions). However, with the new distances, the distribution of stellar luminosities became more continuous than obtained previously. The hydrogen-showing stars of late WN subtype are still found to be typically more luminous than the hydrogen-free early subtypes, but there is a range of luminosities where both subclasses overlap. The empirical HRD of the Galactic single WN stars is compared with recent evolutionary tracks. Neither these single-star evolutionary models nor binary scenarios can provide a fully satisfactory explanation for the parameters of these objects and their location in the HRD. KW - stars: mass-loss KW - stars: winds, outflows KW - stars: Wolf-Rayet KW - stars: atmospheres KW - stars: evolution KW - stars: distances Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201834850 SN - 1432-0746 VL - 625 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Sander, Andreas Alexander Christoph A1 - Hamann, Wolf-Rainer A1 - Todt, Helge Tobias A1 - Hainich, Rainer A1 - Shenar, Tomer A1 - Ramachandran, Varsha A1 - Oskinova, Lida T1 - The Galactic WC and WO stars BT - The impact of revised distances from Gaia DR2 and their role as massive black hole progenitors JF - Astronomy and astrophysics : an international weekly journal N2 - Wolf-Rayet stars of the carbon sequence (WC stars) are an important cornerstone in the late evolution of massive stars before their core collapse. As core-helium burning, hydrogen-free objects with huge mass-loss, they are likely the last observable stage before collapse and thus promising progenitor candidates for type Ib/c supernovae. Their strong mass-loss furthermore provides challenges and constraints to the theory of radiatively driven winds. Thus, the determination of the WC star parameters is of major importance for several astrophysical fields. With Gaia DR2, for the first time parallaxes for a large sample of Galactic WC stars are available, removing major uncertainties inherent to earlier studies. In this work, we re-examine a previously studied sample of WC stars to derive key properties of the Galactic WC population. All quantities depending on the distance are updated, while the underlying spectral analyzes remain untouched. Contrasting earlier assumptions, our study yields that WC stars of the same subtype can significantly vary in absolute magnitude. With Gaia DR2, the picture of the Galactic WC population becomes more complex: We obtain luminosities ranging from log L/L-circle dot = 4.9-6.0 with one outlier (WR 119) having log L/L-circle dot = 4.7. This indicates that the WC stars are likely formed from a broader initial mass range than previously assumed. We obtain mass-loss rates ranging between log(M) over dot = -5.1 and -4.1, with (M) over dot proportional to L-0.68 and a linear scaling of the modified wind momentum with luminosity. We discuss the implications for stellar evolution, including unsolved issues regarding the need of envelope inflation to address the WR radius problem, and the open questions in regard to the connection of WR stars with Gamma-ray bursts. WC and WO stars are progenitors of massive black holes, collapsing either silently or in a supernova that most-likely has to be preceded by a WO stage. KW - stars: evolution KW - stars: mass-loss KW - stars: Wolf-Rayet KW - stars: massive KW - stars: distances KW - Galaxy: stellar content Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201833712 SN - 1432-0746 VL - 621 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Hubrig, Swetlana A1 - Kholtygin, A. A1 - Ilyin, Ilya A1 - Schöller, M. A1 - Oskinova, Lida T1 - THE FIRST SPECTROPOLARIMETRIC MONITORING OF THE PECULIAR O4 Ief SUPERGIANT zeta PUPPIS JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The origin of the magnetic field in massive O-type stars is still under debate. To model the physical processes responsible for the generation of O star magnetic fields, it is important to understand whether correlations between the presence of a magnetic field and stellar evolutionary state, rotation velocity, kinematical status, and surface composition can be identified. The O4 Ief supergiant zeta Pup is a fast rotator and a runaway star, which may be a product of a past binary interaction, possibly having had an encounter with the cluster Trumper 10 some 2 Myr ago. The currently available observational material suggests that certain observed phenomena in this star may be related to the presence of a magnetic field. We acquired spectropolarimetric observations of zeta Pup with FORS 2 mounted on the 8 m Antu telescope of the Very Large Telescope to investigate if a magnetic field is indeed present in this star. We show that many spectral lines are highly variable and probably vary with the recently detected period of 1.78 day. No magnetic field is detected in zeta Pup, as no magnetic field measurement has a significance level higher than 2.4 sigma. Still, we studied the probability of a single sinusoidal explaining the variation of the longitudinal magnetic field measurements. KW - stars: atmospheres KW - stars: early-type KW - stars: individual (zetaPup) KW - stars: magnetic field KW - stars: variables: general Y1 - 2016 U6 - https://doi.org/10.3847/0004-637X/822/2/104 SN - 0004-637X SN - 1538-4357 VL - 822 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Pillitteri, Ignazio A1 - Wolk, Scott J. A1 - Reale, Fabio A1 - Oskinova, Lida T1 - The early B-type star Rho Ophiuchi A is an X-ray lighthouse JF - Astronomy and astrophysics : an international weekly journal N2 - We present the results of a 140 ks XMM-Newton observation of the B2 star rho Oph A. The star has exhibited strong X-ray variability: a cusp-shaped increase of rate, similar to that which we partially observed in 2013, and a bright flare. These events are separated in time by about 104 ks, which likely correspond to the rotational period of the star (1.2 days). Time resolved spectroscopy of the X-ray spectra shows that the first event is caused by an increase of the plasma emission measure, while the second increase of rate is a major flare with temperatures in excess of 60 MK (kT similar to 5 keV). From the analysis of its rise, we infer a magnetic field of >= 300 G and a size of the flaring region of similar to 1.4-1.9 x 10(11) cm, which corresponds to similar to 25%-30% of the stellar radius. We speculate that either an intrinsic magnetism that produces a hot spot on its surface or an unknown low mass companion are the source of such X-rays and variability. A hot spot of magnetic origin should be a stable structure over a time span of >= 2.5 yr, and suggests an overall large scale dipolar magnetic field that produces an extended feature on the stellar surface. In the second scenario, a low mass unknown companion is the emitter of X-rays and it should orbit extremely close to the surface of the primary in a locked spin-orbit configuration, almost on the verge of collapsing onto the primary. As such, the X-ray activity of the secondary star would be enhanced by its young age, and the tight orbit as in RS Cvn systems. In both cases rho Oph would constitute an extreme system that is worthy of further investigation. KW - stars: activity KW - stars: individual: Rho Ophiuchi KW - stars: early-type KW - stars: magnetic field KW - starspots KW - X-rays: stars Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201630070 SN - 1432-0746 VL - 602 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Leto, Paolo A1 - Trigilio, C. A1 - Oskinova, Lida A1 - Ignace, R. A1 - Buemi, C. S. A1 - Umana, G. A1 - Ingallinera, A. A1 - Todt, Helge Tobias A1 - Leone, F. T1 - The detection of variable radio emission from the fast rotating magnetic hot B-star HR 7355 and evidence for its X-ray aurorae JF - Monthly notices of the Royal Astronomical Society N2 - In this paper, we investigate the multiwavelength properties of the magnetic early B-type star HR 7355. We present its radio light curves at several frequencies, taken with the Jansky Very Large Array, and X-ray spectra, taken with the XMM-Newton X-ray telescope. Modelling of the radio light curves for the Stokes I and V provides a quantitative analysis of the HR 7355 magnetosphere. A comparison between HR 7355 and a similar analysis for the Ap star CU Vir allows us to study how the different physical parameters of the two stars affect the structure of the respective magnetospheres where the non-thermal electrons originate. Our model includes a cold thermal plasma component that accumulates at high magnetic latitudes that influences the radio regime, but does not give rise to X-ray emission. Instead, the thermal X-ray emission arises from shocks generated by wind stream collisions close to the magnetic equatorial plane. The analysis of the X-ray spectrum of HR 7355 also suggests the presence of a non-thermal radiation. Comparison between the spectral index of the power-law X-ray energy distribution with the non-thermal electron energy distribution indicates that the non-thermal X-ray component could be the auroral signature of the non-thermal electrons that impact the stellar surface, the same non-thermal electrons that are responsible for the observed radio emission. On the basis of our analysis, we suggest a novel model that simultaneously explains the X-ray and the radio features of HR 7355 and is likely relevant for magnetospheres of other magnetic early-type stars. KW - stars: chemically peculiar KW - stars: early-type KW - stars: individual: HR 7355 KW - stars: magnetic field KW - radio continuum: stars KW - X-rays: stars Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx267 SN - 0035-8711 SN - 1365-2966 VL - 467 SP - 2820 EP - 2833 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Oskinova, Lida A1 - Ignace, Richard A1 - Hamann, Wolf-Rainer A1 - Pollock, A. M. T. A1 - Brown, John C. T1 - The conspicuous absence of X-ray emission from carbon-enriched Wolf-Rayet stars N2 - The carbon-rich WC5 star WR 114 was not detected during a 15.9 ksec XMM-Newton observation, implying an upper limit to the X-ray luminosity of Lx < 2.5 x 1030 ergs-1 and to the X-ray to bolometric luminosity ratio of Lx/Lbol < 4 x 10-9. This confirms indications from earlier less sensitive measurements that there has been no convincing X-ray detection of any single WC star. This lack of detections is reinforced by XMM-Newton and CHANDRA observations of WC stars. Thus the conclusion has to be drawn that the stars with radiatively-driven stellar winds of this particular class are insignificant X-ray sources. We attribute this to photoelectronic absorption by the stellar wind. The high opacity of the metal-rich and dense winds from WC stars puts the radius of optical depth unity at hundreds or thousands of stellar radii for much of the X-ray band. We believe that the essential absence of hot plasma so far out in the wind exacerbated by the large distances and correspondingly high ISM column densities makes the WC stars too faint to be detectable with current technology. The result also applies to many WC stars in binary systems, of which only about 20 % are identified X-ray sources, presumably due to colliding winds. Y1 - 2003 ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Guerrero, Martín A. A1 - Todt, Helge Tobias A1 - Hamann, Wolf-Rainer A1 - Chu, Y.-H. A1 - Gruendl, R. A. A1 - Schönberner, Detlef A1 - Oskinova, Lida A1 - Marquez-Lugo, R. A. A1 - Fang, X. A1 - Ramos-Larios, Gerardo T1 - The born-again Planetary nebula A78: an X-RAY twin of A30 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present the XMM-Newton discovery of X-ray emission from the planetary nebula (PN) A78, the second born-again PN detected in X-rays apart from A30. These two PNe share similar spectral and morphological characteristics: they harbor diffuse soft X-ray emission associated with the interaction between the H-poor ejecta and the current fast stellar wind and a point-like source at the position of the central star (CSPN). We present the spectral analysis of the CSPN, using for the first time an NLTE code for expanding atmospheres that takes line blanketing into account for the UV and optical spectra. The wind abundances are used for the X-ray spectral analysis of the CSPN and the diffuse emission. The X-ray emission from the CSPN in A78 can be modeled by a single C VI emission line, while the X-ray emission from its diffuse component is better described by an optically thin plasma emission model with a temperature of kT = 0.088 keV (T approximate to 1.0 x 10(6) K). We estimate X-ray luminosities in the 0.2-2.0 keV energy band of L-X,L-CSPN =(1.2 +/- 0.3) x 10(31) erg s(-1) and L-X,L-DIFF =(9.2 +/- 2.3) x 10(30) erg s(-1) for the CSPN and diffuse components, respectively. KW - planetary nebulae: general KW - planetary nebulae: individual (A78) KW - stars: winds, outflows KW - X-rays: ISM Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/799/1/67 SN - 0004-637X SN - 1538-4357 VL - 799 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Morel, T. A1 - Castro, Norberto A1 - Fossati, Luca A1 - Hubrig, Swetlana A1 - Langer, N. A1 - Przybilla, Norbert A1 - Schöller, Markus A1 - Carroll, Thorsten Anthony A1 - Ilyin, Ilya A1 - Irrgang, Andreas A1 - Oskinova, Lida A1 - Schneider, Fabian R. N. A1 - Simon Díaz, Sergio A1 - Briquet, Maryline A1 - González, Jean-Francois A1 - Kharchenko, Nina A1 - Nieva, M.-F. A1 - Scholz, Ralf-Dieter A1 - de Koter, Alexander A1 - Hamann, Wolf-Rainer A1 - Herrero, Artemio A1 - Maíz Apellániz, Jesus A1 - Sana, Hugues A1 - Arlt, Rainer A1 - Barbá, Rodolfo H. A1 - Dufton, Polly A1 - Kholtygin, Alexander A1 - Mathys, Gautier A1 - Piskunov, Anatoly E. A1 - Reisenegger, Andreas A1 - Spruit, H. A1 - Yoon, S.-C. T1 - The B fields in OB stars (BOB) survey T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 821 KW - magnetic fields KW - stars: early-type KW - stars: magnetic fields KW - stars: individual (HD 164492C, CPD –57 ◦ 3509, HD 54879, β CMa, ε CMa) Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-415238 SN - 1866-8372 IS - 821 ER - TY - JOUR A1 - Bozzo, Enrico A1 - Bernardini, F. A1 - Ferrigno, Carlo A1 - Falanga, M. A1 - Romano, Patrizia A1 - Oskinova, Lida T1 - The accretion environment of supergiant fast X-ray transients probed with XMM-Newton JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Supergiant fast X-ray (SFXT) transients are a peculiar class of supergiant X-ray binaries characterized by a remarkable variability in the X-ray domain, widely ascribed to accretion from a clumpy stellar wind. Aims. In this paper we performed a systematic and homogeneous analysis of the sufficiently bright X-ray flares observed with XMM-Newton from the supergiant fast X-ray transients to probe spectral variations on timescales as short as a few hundred seconds. Our ultimate goal is to investigate whether SFXT flares and outbursts are triggered by the presence of clumps, and to reveal whether strongly or mildly dense clumps are required. Methods. For all sources, we employ a technique developed by our group already exploited in a number of our previous papers, making use of an adaptive rebinned hardness ratio to optimally select the time intervals for the spectral extraction. A total of twelve observations performed in the direction of five SFXTs are reported, providing the largest sample of events available so far. Results. Using the original results reported here and those obtained with our technique from the analysis of two previously published XMM-Newton observations of IGR J17544-2619 and IGR J18410-0535, we show that both strongly and mildly dense clumps can trigger these events. In the former case, the local absorption column density may increase by a factor of >> 3, while in the latter case, the increase is only a factor of similar to 2-3 (or lower). An increase in the absorption column density is generally recorded during the rise of the flares/outbursts, while a drop follows when the source achieves peak flux. In a few cases, a re-increase of the absorption column density after the flare is also detected, and we discovered one absorption event related to the passage of an unaccreted clump in front of the compact object. Overall, there seems to be no obvious correlation between the dynamic ranges in the X-ray fluxes and absorption column densities in supergiant fast X-ray transients, with an indication that lower densities are recorded at the highest fluxes. Conclusions. The spectral variations measured in all sources are in agreement with the idea that the flares/outbursts are triggered by the presence of dense structures in the wind interacting with the X-rays from the compact object (leading to photoionization). The lack of correlation between the dynamic ranges in the X-ray fluxes and absorption column densities can be explained by the presence of accretion inhibition mechanism(s). Based on the knowledge acquired so far on the SFXTs, we propose a classification of the flares/outbursts from these sources in order to drive future observational investigations. We suggest that the difference between the classes of flares/outbursts is related to the fact that the mechanism(s) inhibiting accretion can be overcome more easily in some sources compared to others. We also investigate the possibility that different stellar wind structures, other than clumps, could provide the means to temporarily overcome the inhibition of accretion in supergiant fast X-ray transients. KW - X-rays: individuals: IGRJ18450-0435 KW - X-rays: individuals: IGRJ17544-2619 KW - X-rays: binaries KW - X-rays: individuals: SAXJ1818.6-1703 KW - X-rays: individuals: IGRJ17354-3255 KW - X-rays: individuals: IGRJ16328-4726 Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201730398 SN - 1432-0746 VL - 608 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Fulmer, Leah M. A1 - Gallagher, John S. A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Ramachandran, Varsha T1 - Testing massive star evolution, star-formation history, and feedback at low metallicity BT - photometric analysis of OB stars in the SMC Wing JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The supergiant ionized shell SMC-SGS 1 (DEM 167), which is located in the outer Wing of the Small Magellanic Cloud (SMC), resembles structures that originate from an energetic star-formation event and later stimulate star formation as they expand into the ambient medium. However, stellar populations within and surrounding SMC-SGS 1 tell a different story. Aims. We present a photometric study of the stellar population encompassed by SMC-SGS 1 in order to trace the history of such a large structure and its potential influence on star formation within the low-density, low-metallicity environment of the SMC. Methods. For a stellar population that is physically associated with SMC-SGS 1, we combined near-ultraviolet (NUV) photometry from the Galaxy Evolution Explorer with archival optical (V-band) photometry from the ESO Danish 1.54 m Telescope. Given their colors and luminosities, we estimated stellar ages and masses by matching observed photometry to theoretical stellar isochrone models. Results. We find that the investigated region supports an active, extended star-formation event spanning similar to 25-40 Myr ago, as well as continued star formation into the present. Using a standard initial mass function, we infer a lower bound on the stellar mass from this period of similar to 3 x 10(4) M-circle dot, corresponding to a star-formation intensity of similar to 6 x 10(-3) M-circle dot kpc(-2) yr(-1). Conclusions. The spatial and temporal distributions of young stars encompassed by SMC-SGS 1 imply a slow, consistent progression of star formation over millions of years. Ongoing star formation, both along the edge and interior to SMC-SGS 1, suggests a combined stimulated and stochastic mode of star formation within the SMC Wing. We note that a slow expansion of the shell within this low-density environment may preserve molecular clouds within the volume of the shell, leaving them to form stars even after nearby stellar feedback expels local gas and dust. KW - galaxies KW - stellar content KW - stars KW - formation KW - individual KW - Small KW - Magellanic Cloud Y1 - 2020 U6 - https://doi.org/10.1051/0004-6361/201834314 SN - 0004-6361 SN - 1432-0746 VL - 633 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Ramachandran, Varsha A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Gallagher, J. S. A1 - Hainich, Rainer A1 - Shenar, Tomer A1 - Sander, Andreas Alexander Christoph A1 - Todt, Helge Tobias A1 - Fulmer, Leah M. T1 - Testing massive star evolution, star formation history, and feedback at low metallicity BT - Spectroscopic analysis of OB stars in the SMC Wing JF - Astronomy and astrophysics : an international weekly journal N2 - Stars that start their lives with spectral types O and early B are the progenitors of core-collapse supernovae, long gamma-ray bursts, neutron stars, and black holes. These massive stars are the primary sources of stellar feedback in star-forming galaxies. At low metallicities, the properties of massive stars and their evolution are not yet fully explored. Here we report a spectroscopic study of 320 massive stars of spectral types O (23 stars) and B (297 stars) in the Wing of the Small Magellanic Cloud (SMC). The spectra, which we obtained with the ESO Very Large Telescope, were analyzed using state-of-the-art stellar atmosphere models, and the stellar parameters were determined. We find that the stellar winds of our sample stars are generally much weaker than theoretically expected. The stellar rotation rates show broad, tentatively bimodal distributions. The upper Hertzsprung-Russell diagram (HRD) is well populated by the stars of our sample from a specific field in the SMC Wing. A few very luminous O stars are found close to the main sequence, while all other, slightly evolved stars obey a strict luminosity limit. Considering additional massive stars in evolved stages, with published parameters and located all over the SMC, essentially confirms this picture. The comparison with single-star evolutionary tracks suggests a dichotomy in the fate of massive stars in the SMC. Only stars with an initial mass below similar to 30 M-circle dot seem to evolve from the main sequence to the cool side of the HRD to become a red supergiant and to explode as type II-P supernova. In contrast, stars with initially more than similar to 30 M-circle dot appear to stay always hot and might evolve quasi chemically homogeneously, finally collapsing to relatively massive black holes. However, we find no indication that chemical mixing is correlated with rapid rotation. We measured the key parameters of stellar feedback and established the links between the rates of star formation and supernovae. Our study demonstrates that in metal-poor environments stellar feedback is dominated by core-collapse supernovae in combination with winds and ionizing radiation supplied by a few of the most massive stars. We found indications of the stochastic mode of massive star formation, where the resulting stellar population is fully capable of producing large-scale structures such as the supergiant shell SMC-SGS 1 in the Wing. The low level of feedback in metal-poor stellar populations allows star formation episodes to persist over long timescales. KW - stars: evolution KW - stars: massive KW - stars: mass-loss KW - Magellanic Clouds KW - Hertzsprung-Russell and C-M diagrams KW - techniques: spectroscopic Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201935365 SN - 1432-0746 VL - 625 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Ramachandran, Varsha A1 - Hainich, Rainer A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Shenar, T. A1 - Sander, Andreas Alexander Christoph A1 - Todt, Helge Tobias A1 - Gallagher, John S. T1 - Stellar population of the superbubble N206 in the LMC I. Analysis of the Of-type stars JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Massive stars severely influence their environment by their strong ionizing radiation and by the momentum and kinetic energy input provided by their stellar winds and supernovae. Quantitative analyses of massive stars are required to understand how their feedback creates and shapes large scale structures of the interstellar medium. The giant H II region N206 in the Large Magellanic Cloud contains an OB association that powers a superbubble filled with hot X-ray emitting gas, serving as an ideal laboratory in this context. Aims. We aim to estimate stellar and wind parameters of all OB stars in N206 by means of quantitative spectroscopic analyses. In this first paper, we focus on the nine Of-type stars located in this region. We determine their ionizing flux and wind mechanical energy. The analysis of nitrogen abundances in our sample probes rotational mixing. Methods. We obtained optical spectra with the multi-object spectrograph FLAMES at the ESO-VLT. When possible, the optical spectroscopy was complemented by UV spectra from the HST, IUE, and FUSE archives. Detailed spectral classifications are presented for our sample Of-type stars. For the quantitative spectroscopic analysis we used the Potsdam Wolf-Rayet model atmosphere code. We determined the physical parameters and nitrogen abundances of our sample stars by fitting synthetic spectra to the observations. Results. The stellar and wind parameters of nine Of-type stars, which are largely derived from spectral analysis are used to construct wind momentum luminosity relationship. We find that our sample follows a relation close to the theoretical prediction, assuming clumped winds. The most massive star in the N206 association is an Of supergiant that has a very high mass-loss rate. Two objects in our sample reveal composite spectra, showing that the Of primaries have companions of late O subtype. All stars in our sample have an evolutionary age of less than 4 million yr, with the O2-type star being the youngest. All these stars show a systematic discrepancy between evolutionary and spectroscopic masses. All stars in our sample are nitrogen enriched. Nitrogen enrichment shows a clear correlation with increasing projected rotational velocities. Conclusions. The mechanical energy input from the Of stars alone is comparable to the energy stored in the N206 superbubble as measured from the observed X-ray and H alpha emission. KW - stars: early-type KW - Magellanic Clouds KW - stars: atmospheres KW - stars: winds, outflows KW - stars: mass-loss KW - stars: massive Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201731093 SN - 1432-0746 SN - 0004-6361 VL - 609 PB - EDP Sciences CY - Les Ulis ER - TY - CHAP A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Feldmeier, Achim T1 - Spectrum formation in clumpy stellar winds N2 - Modeling expanding atmospheres is a difficult task because of the extreme non-LTE situation, the need to account for complex model atoms, especially for the iron-group elements with their millions of lines, and because of the supersonic expansion. Adequate codes have been developed e.g. by Hillier (CMFGEN), the Munich group (Puls, Pauldrach), and in Potsdam (PoWR code, Hamann et al.). While early work was based on the assumption of a smooth and homogeneous spherical stellar wind, the need to account for clumping became obvious about ten years ago. A relatively simple first-order clumping correction was readily implemented into the model codes. However, its simplifying assumptions are severe. Most importantly, the clumps are taken to be optically thin at all frequencies (”microclumping”). We discuss the consequences of this approximation and describe an approach to account for optically thick clumps (“macroclumping”). First results demonstrate that macroclumping can generally reduce the strength of spectral features, depending on their optical thickness. The recently reported discrepancy between the Hα diagnostic and the Pv resonance lines in O star spectra can be resolved without decreasing the mass-loss rates, when macroclumping is taken into account. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17838 ER - TY - JOUR A1 - Hubrig, Swetlana A1 - Scholz, Kathleen A1 - Hamann, Wolf-Rainer A1 - Schoeller, M. A1 - Ignace, R. A1 - Ilyin, Ilya A1 - Gayley, K. G. A1 - Oskinova, Lida T1 - Searching for a magnetic field in Wolf-Rayet stars using FORS 2 spectropolarimetry JF - Monthly notices of the Royal Astronomical Society N2 - To investigate if magnetic fields are present in Wolf-Rayet stars, we selected a few stars in the Galaxy and one in the Large Magellanic Cloud (LMC). We acquired low-resolution spectropolarimetric observations with the European Southern Observatory FORS 2 (FOcal Reducer low dispersion Spectrograph) instrument during two different observing runs. During the first run in visitor mode, we observed the LMC Wolf-Rayet star BAT99 7 and the stars WR 6, WR 7, WR 18, and WR 23 in our Galaxy. The second run in service mode was focused on monitoring the star WR 6. Linear polarization was recorded immediately after the observations of circular polarization. During our visitor observing run, the magnetic field for the cyclically variable star WR 6 was measured at a significance level of 3.3 sigma (< B-z > = 258 +/- 78 G). Among the other targets, the highest value for the longitudinal magnetic field, < B-z > = 327 +/- 141 G, was measured in the LMC star BAT99 7. Spectropolarimetric monitoring of the star WR 6 revealed a sinusoidal nature of the < B-z > variations with the known rotation period of 3.77 d, significantly adding to the confidence in the detection. The presence of the rotation-modulated magnetic variability is also indicated in our frequency periodogram. The reported field magnitude suffers from significant systematic uncertainties at the factor of 2 level, in addition to the quoted statistical uncertainties, owing to the theoretical approach used to characterize it. Linear polarization measurements showed no line effect in the stars, apart from WR 6. BAT99 7, WR 7, and WR 23 do not show variability of the linear polarization over two nights. KW - techniques: polarimetric KW - stars: individual: WR 6 KW - stars: magnetic field KW - stars: variables: general KW - stars: Wolf-Rayet Y1 - 2016 U6 - https://doi.org/10.1093/mnras/stw558 SN - 0035-8711 SN - 1365-2966 VL - 458 SP - 3381 EP - 3393 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Guerrero, Martín A. A1 - Ruiz, N. A1 - Hamann, Wolf-Rainer A1 - Chu, Y.-H. A1 - Todt, Helge Tobias A1 - Schönberner, Detlef A1 - Oskinova, Lida A1 - Gründl, R. A. A1 - Steffen, M. A1 - Blair, William P. A1 - Toala, Jesús Alberto T1 - Rebirth of X-Ray emission from the born-again planetary Nebula A30 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The planetary nebula A30 is believed to have undergone a very late thermal pulse resulting in the ejection of knots of hydrogen-poor material. Using multi-epoch Hubble Space Telescope images, we have detected the angular expansion of these knots and derived an age of 850(-150)(+280) yr. To investigate the spectral and spatial properties of the soft X-ray emission detected by ROSAT, we have obtained Chandra and XMM-Newton deep observations of A30. The X-ray emission from A30 can be separated into two components: a point source at the central star and diffuse emission associated with the hydrogen-poor knots and the cloverleaf structure inside the nebular shell. To help us assess the role of the current stellar wind in powering this X-ray emission, we have determined the stellar parameters and wind properties of the central star of A30 using a non-LTE model fit to its optical and UV spectra. The spatial distribution and spectral properties of the diffuse X-ray emission are highly suggestive that it is generated by the post-born-again and present fast stellar winds interacting with the hydrogen-poor ejecta of the born-again event. This emission can be attributed to shock-heated plasma, as the hydrogen-poor knots are ablated by the stellar winds, under which circumstances the efficient mass loading of the present fast stellar wind raises its density and damps its velocity to produce the observed diffuse soft X-rays. Charge transfer reactions between the ions of the stellar winds and material of the born-again ejecta have also been considered as a possible mechanism for the production of diffuse X-ray emission, and upper limits on the expected X-ray production by this mechanism have been derived. The origin of the X-ray emission from the central star of A30 is puzzling: shocks in the present fast stellar wind and photospheric emission can be ruled out, while the development of a new, compact hot bubble confining the fast stellar wind seems implausible. KW - planetary nebulae: general KW - planetary nebulae: individual (A30) KW - stars: winds, outflows KW - X-rays: ISM Y1 - 2012 U6 - https://doi.org/10.1088/0004-637X/755/2/129 SN - 0004-637X VL - 755 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Huenemoerder, David P. A1 - Gayley, K. G. A1 - Hamann, Wolf-Rainer A1 - Ignace, R. A1 - Nichols, J. S. A1 - Oskinova, Lida A1 - Pollock, A. M. T. A1 - Schulz, Norbert S. A1 - Shenar, Tomer T1 - Probing Wolf-Rayet winds: Chandra/HETG X-ray spectra of WR 6 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. Variability was present in X-rays and simultaneous optical photometry, but neither were correlated with the known period of the system or with each other. An enhanced abundance of sodium revealed nuclear-processed material, a quantity related to the evolutionary state of the star. The characterization of the extent and nature of the hot plasma in WR 6 will help to pave the way to a more fundamental theoretical understanding of the winds and evolution of massive stars. KW - stars: individual (WR 6) KW - stars: massive KW - stars: Wolf-Rayet Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/815/1/29 SN - 0004-637X SN - 1538-4357 VL - 815 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Oskinova, Lida T1 - Preface: X-ray emission from hot stars and their winds T2 - Advances in space research Y1 - 2016 U6 - https://doi.org/10.1016/j.asr.2016.06.031 SN - 0273-1177 SN - 1879-1948 VL - 58 SP - 679 EP - 679 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Hainich, Rainer A1 - Ramachandran, Varsha A1 - Shenar, Tomer A1 - Sander, Andreas Alexander Christoph A1 - Todt, Helge Tobias A1 - Gruner, David A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer T1 - PoWR grids of non-LTE model atmospheres for OB-type stars of various metallicities JF - Astronomy and astrophysics : an international weekly journal N2 - The study of massive stars in different metallicity environments is a central topic of current stellar research. The spectral analysis of massive stars requires adequate model atmospheres. The computation of such models is difficult and time-consuming. Therefore, spectral analyses are greatly facilitated if they can refer to existing grids of models. Here we provide grids of model atmospheres for OB-type stars at metallicities corresponding to the Small and Large Magellanic Clouds, as well as to solar metallicity. In total, the grids comprise 785 individual models. The models were calculated using the state-of-the-art Potsdam Wolf-Rayet (PoWR) model atmosphere code. The parameter domain of the grids was set up using stellar evolution tracks. For all these models, we provide normalized and flux-calibrated spectra, spectral energy distributions, feedback parameters such as ionizing photons, Zanstra temperatures, and photometric magnitudes. The atmospheric structures (the density and temperature stratification) are available as well. All these data are publicly accessible through the PoWR website. KW - stars: massive KW - stars: early-type KW - stars: atmospheres KW - stars: winds KW - outflows KW - stars: mass-loss KW - radiative transfer Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201833787 SN - 1432-0746 VL - 621 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Feldmeier, Achim A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Owocki, S. P. T1 - Overloaded and fractured winds N2 - We discuss the connection between wind overloading and discrete absorption components in P Cygni line profiles from O stars. Overloading can create horizontal plateaus in the radial wind speed that cause the extra absorption in the line profile. The upstream propagation speed of these velocity plateaus is analyzed. The second part of the paper deals with X-ray emission from O stars. X-ray line profiles observed with Chandra and XMM are often symmetric, contrary to what is expected for lines from a homogeneous wind. We discuss the influence on line symmetry of photon escape channels in a strongly clumped wind. Y1 - 2003 SN - 1-58381-133-8 ER - TY - JOUR A1 - Oskinova, Lida A1 - Todt, Helge Tobias A1 - Huenemoerder, David P. A1 - Hubrig, Swetlana A1 - Ignace, Richard A1 - Hamann, Wolf-Rainer A1 - Balona, Luis T1 - On X-ray pulsations in beta Cephei-type variables JF - Astronomy and astrophysics : an international weekly journal N2 - Context. beta Cep-type variables are early B-type stars that are characterized by oscillations observable in their optical light curves. At least one beta Cep-variable also shows periodic variability in X-rays. Aims. Here we study the X-ray light curves in a sample of beta Cep-variables to investigate how common X-ray pulsations are for this type of stars. Methods. We searched the Chandra and XMM-Newton X-ray archives and selected stars that were observed by these telescopes for at least three optical pulsational periods. We retrieved and analyzed the X-ray data for kappa Sco, beta Cru, and alpha Vir. The X-ray light curves of these objects were studied to test for their variability and periodicity. Results. While there is a weak indication for X-ray variability in beta Cru, we find no statistically significant evidence of X-ray pulsations in any of our sample stars. This might be due either to the insufficient data quality or to the physical lack of modulations. New, more sensitive observations should settle this question. KW - stars: massive KW - stars: variables: general KW - X-rays: stars Y1 - 2015 U6 - https://doi.org/10.1051/0004-6361/201525908 SN - 0004-6361 SN - 1432-0746 VL - 577 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Hünemörder, David P. A1 - Oskinova, Lida A1 - Ignace, Richard A1 - Waldron, Wayne L. A1 - Todt, Helge Tobias A1 - Hamaguchi, Kenji A1 - Kitamoto, Shunji T1 - On the weak-wind problem in massive stars X-ray spectra reveal a massive hot wind in mu columbaea JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"-identified from cool wind UV/optical spectra-is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays. KW - stars: early-type KW - stars: individual (mu Col) KW - stars: mass-loss KW - X-rays: stars Y1 - 2012 U6 - https://doi.org/10.1088/2041-8205/756/2/L34 SN - 2041-8205 VL - 756 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Hamann, Wolf-Rainer A1 - Brown, John C. A1 - Feldmeier, Achim A1 - Oskinova, Lida T1 - On the wavelength drift of spectral features from structured hot star winds N2 - Spectral lines formed in stellar winds from OB stars are observed to exhibit profile variations. Discrete Absorption Components (DACs) show a remarkably slow wavelength drift with time. In a straightforward interpretation, this is in sharp contradiction to the steep velocity law predicted by the radiation-driven wind theory, and by semi- empirical profile fitting. In the present paper we re-discuss the interpretation of the drift rate. We show that the Co- rotating Interaction Region (CIR) model for the formation of DACs does not explain their slow drift rate as a consequence of rotation. On the contrary, the apparent acceleration of a spectral CIR feature is even higher than for the corresponding kinematical model without rotation. However, the observations can be understood by distinguishing between the velocity field of the matter flow, and the velocity law for the motion of the patterns in which the DAC features are formed. If the latter propagate upstream against the matter flow, the resulting wavelength drift mimics a much slower acceleration although the matter is moving fast. Additional to the DACs, a second type of recurrent structures is present in observed OB star spectra, the so-called modulations. In contrast to the DACs, these structures show a steep acceleration compatible with the theoretically predicted velocity law. We see only two possible consistent scenarios. Either, the wind is accelerated fast, and the modulations are formed in advected structures, while the DACs come from structures which are propagating upstream. Or, alternatively, steep and shallow velocity laws may co-exist at the same time in different spatial regions or directions of the wind. Y1 - 2001 ER - TY - JOUR A1 - Torrejon, Jose M. A1 - Schulz, Norbert S. A1 - Nowak, Michael A. A1 - Oskinova, Lida A1 - Rodes-Roca, Jose J. A1 - Shenar, Tomer A1 - Wilms, Jörn T1 - On the radial onset of clumping in the wind of the B0I massive star QV nor JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present an analysis of a 78 ks Chandra high-energy transmission gratings observation of the B0I star QV Nor, the massive donor of the wind-accreting pulsar 4U1538-52. The neutron star (NS) orbits its companion in a very close orbit (r < 1.4R(*), in units of the stellar radii), thereby allowing probing of the innermost wind regions. The flux of the Fe K alpha line during eclipse reduces to only similar to 30% of the flux measured out of eclipse. This indicates that the majority of Fe fluorescence must be produced in regions close to the NS, at distances smaller than 1R(*) from its surface. The fact that the flux of the continuum decreases to only similar to 3% during eclipse allows for a high contrast of the Fe Ka line fluorescence during eclipse. The line is not resolved and centered at lambda = 1.9368(-0.0018)(+0.0032) angstrom. From the inferred plasma speed limit of v < c Delta lambda/lambda < 800 km s(-1) and range of ionization parameters of log xi =[-1, 2], together with the stellar density profile, we constrain the location of the cold, dense material in the stellar wind of QV Nor using simple geometrical considerations. We then use the Fe K alpha line fluorescence as a tracer of wind clumps and determine that these clumps in the stellar wind of QV Nor (B0I) must already be present at radii r < 1.25R(*), close to the photosphere of the star. KW - stars: individual (QV Nor, 4U1538+52) KW - stars: winds, outflows KW - X-rays: binaries Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/810/2/102 SN - 0004-637X SN - 1538-4357 VL - 810 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Oskinova, Lida A1 - Huenemoerder, D. P. A1 - Hamann, Wolf-Rainer A1 - Shenar, Tomer A1 - Sander, Andreas Alexander Christoph A1 - Ignace, R. A1 - Todt, Helge Tobias A1 - Hainich, Rainer T1 - On the Binary Nature of Massive Blue Hypergiants: High-resolution X-Ray Spectroscopy Suggests That Cyg OB2 12 is a Colliding Wind Binary JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - The blue hypergiant Cyg OB2 12 (B3Ia(+)) is a representative member of the class of very massive stars in a poorly understood evolutionary stage. We obtained its high-resolution X-ray spectrum using the Chandra observatory. PoWR model atmospheres were calculated to provide realistic wind opacities and to establish the wind density structure. We find that collisional de-excitation is the dominant mechanism depopulating the metastable upper levels of the forbidden lines of the He-like ions Si XIV and Mg XII. Comparison between the model and observations reveals that X-ray emission is produced in a dense plasma, which could reside only at the photosphere or in a colliding wind zone between binary components. The observed X-ray spectra are well-fitted by thermal plasma models, with average temperatures in excess of 10 MK. The wind speed in Cyg OB2 12 is not high enough to power such high temperatures, but the collision of two winds in a binary system can be sufficient. We used archival data to investigate the X-ray properties of other blue hypergiants. In general, stars of this class are not detected as X-ray sources. We suggest that our new Chandra observations of Cyg OB2 12 can be best explained if Cyg OB2 12 is a colliding wind binary possessing a late O-type companion. This makes Cyg OB2 12 only the second binary system among the 16 known Galactic hypergiants. This low binary fraction indicates that the blue hypergiants are likely products of massive binary evolution during which they either accreted a significant amount of mass or already merged with their companions. KW - stars: individual (Cyg OB2 12) KW - stars: massive KW - stars: mass-loss KW - stars: winds, outflows KW - supergiants KW - X-rays: stars Y1 - 2017 U6 - https://doi.org/10.3847/1538-4357/aa7e79 SN - 0004-637X SN - 1538-4357 VL - 845 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Ignace, Richard A1 - Sander, Andreas Alexander Christoph A1 - Shenar, Tomer A1 - Todt, Helge Tobias A1 - Chu, Y. -H. A1 - Guerrero, Martin A. A1 - Hainich, Rainer A1 - Torrejon, Jose Miguel T1 - On the Apparent Absence of Wolf-Rayet plus Neutron Star Systems BT - the Curious Case of WR124 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - Among the different types of massive stars in advanced evolutionary stages is the enigmatic WN8h type. There are only a few Wolf-Rayet (WR) stars with this spectral type in our Galaxy. It has long been suggested that WN8h-type stars are the products of binary evolution that may harbor neutron stars (NS). One of the most intriguing WN8h stars is the runaway WR 124 surrounded by its magnificent nebula M1-67. We test the presence of an accreting NS companion in WR 124 using similar to 100 ks long observations by the Chandra X-ray observatory. The hard X-ray emission from WR 124 with a luminosity of L-X similar to 10(31) erg s(-1) is marginally detected. We use the non-local thermodynamic equilibrium stellar atmosphere code PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star is effectively opaque for X-rays, hence the low X-ray luminosity of WR 124 does not rule out the presence of an embedded compact object. We suggest that, in general, high-opacity WR winds could prevent X-ray detections of embedded NS, and be an explanation for the apparent lack of WR+NS systems. KW - circumstellar matter KW - ISM: jets and outflows KW - stars: massive KW - stars: evolution KW - stars: neutron KW - stars: Wolf-Rayet Y1 - 2018 U6 - https://doi.org/10.3847/2041-8213/aaf39d SN - 2041-8205 SN - 2041-8213 VL - 869 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Toala, Jesús Alberto A1 - Oskinova, Lida A1 - Ignace, R. T1 - On the Absence of Non-thermal X-Ray Emission around Runaway O Stars JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - Theoretical models predict that the compressed interstellar medium around runaway O stars can produce highenergy non-thermal diffuse emission, in particular, non-thermal X-ray and gamma-ray emission. So far, detection of nonthermal X-ray emission was claimed for only one runaway star, AE Aur. We present a search for non-thermal diffuse X-ray emission from bow shocks using archived XMM-Newton observations for a clean sample of six welldetermined runaway O stars. We find that none of these objects present diffuse X-ray emission associated with their bow shocks, similarly to previous X-ray studies toward. zeta ph and BD+ 43 degrees 3654. We carefully investigated multi-wavelength observations of AE Aur and could not confirm previous findings of non-thermal X-rays. We conclude that so far there is no clear evidence of non-thermal extended emission in bow shocks around runaway O stars. KW - stars: massive KW - stars: mass-loss KW - stars: winds, outflows KW - X-rays: ISM Y1 - 2017 U6 - https://doi.org/10.3847/2041-8213/aa667c SN - 2041-8205 SN - 2041-8213 VL - 838 SP - 1 EP - 32 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Hainich, Rainer A1 - Oskinova, Lida A1 - Shenar, Tomer A1 - Marchant Campos, Pablo A1 - Eldridge, J. J. A1 - Sander, Andreas Alexander Christoph A1 - Hamann, Wolf-Rainer A1 - Langer, Norbert A1 - Todt, Helge Tobias T1 - Observational properties of massive black hole binary progenitors JF - Astronomy and astrophysics : an international weekly journal N2 - Context: The first directly detected gravitational waves (GW 150914) were emitted by two coalescing black holes (BHs) with masses of ≈ 36 M⊙ and ≈ 29 M⊙. Several scenarios have been proposed to put this detection into an astrophysical context. The evolution of an isolated massive binary system is among commonly considered models. Aims: Various groups have performed detailed binary-evolution calculations that lead to BH merger events. However, the question remains open as to whether binary systems with the predicted properties really exist. The aim of this paper is to help observers to close this gap by providing spectral characteristics of massive binary BH progenitors during a phase where at least one of the companions is still non-degenerate. Methods: Stellar evolution models predict fundamental stellar parameters. Using these as input for our stellar atmosphere code (Potsdam Wolf-Rayet), we compute a set of models for selected evolutionary stages of massive merging BH progenitors at different metallicities. Results: The synthetic spectra obtained from our atmosphere calculations reveal that progenitors of massive BH merger events start their lives as O2-3V stars that evolve to early-type blue supergiants before they undergo core-collapse during the Wolf-Rayet phase. When the primary has collapsed, the remaining system will appear as a wind-fed high-mass X-ray binary. Based on our atmosphere models, we provide feedback parameters, broad band magnitudes, and spectral templates that should help to identify such binaries in the future. Conclusions: While the predicted parameter space for massive BH binary progenitors is partly realized in nature, none of the known massive binaries match our synthetic spectra of massive BH binary progenitors exactly. Comparisons of empirically determined mass-loss rates with those assumed by evolution calculations reveal significant differences. The consideration of the empirical mass-loss rates in evolution calculations will possibly entail a shift of the maximum in the predicted binary-BH merger rate to higher metallicities, that is, more candidates should be expected in our cosmic neighborhood than previously assumed. KW - gravitational waves KW - binaries: close KW - stars: early-type KW - stars: atmospheres KW - stars: winds KW - outflows KW - stars: mass-loss Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201731449 SN - 1432-0746 VL - 609 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Torrejon, J. M. A1 - Reig, Pablo A1 - Fürst, F. A1 - Martinez-Chicharro, M. A1 - Postnov, K. A1 - Oskinova, Lida T1 - NuSTAR rules out a cyclotron line in the accreting magnetar candidate 4U2206+54 JF - Monthly notices of the Royal Astronomical Society N2 - Based on our new NuSTAR X-ray telescope data, we rule out any cyclotron line up to 60 keV in the spectra of the high-mass X-ray binary 4U2206+54. In particular, we do not find any evidence of the previously claimed line around 30 keV, independently of the source flux, along the spin pulse. The spin period has increased significantly, since the last observation, up to 5750 +/- 10 s, confirming the rapid spin-down rate (nu)over dot = -1.8 x 10(-14) Hz s(-1). This behaviour might be explained by the presence of a strongly magnetized neutron star (B-s > several times 10(13) G) accreting from the slow wind of its main-sequence O9.5 companion. KW - Stars: individual: 4U2206+54, BD+53 2790 KW - X-rays: binaries Y1 - 2018 U6 - https://doi.org/10.1093/mnras/sty1628 SN - 0035-8711 SN - 1365-2966 VL - 479 IS - 3 SP - 3366 EP - 3372 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Hubrig, Swetlana A1 - Schöller, Markus A1 - Kholtygin, Alexander F. A1 - Tsumura, Hiroki A1 - Hoshino, Akio A1 - Kitamoto, Shunji A1 - Oskinova, Lida A1 - Ignace, Richard A1 - Todt, Helge Tobias A1 - Ilyin, Ilya T1 - New multiwavelength observations of the Of?p star CPD-28 degrees 2561 JF - Monthly notices of the Royal Astronomical Society N2 - A rather strong mean longitudinal magnetic field of the order of a few hundred gauss was detected a few years ago in the Of?p star CPD -28 degrees 2561 using FORS2 (FOcal Reducer low dispersion Spectrograph 2) low-resolution spectropolarimetric observations. In this work, we present additional low-resolution spectropolarimetric observations obtained during several weeks in 2013 December using FORS 2 mounted at the 8-m Antu telescope of the Very Large Telescope (VLT). These observations cover a little less than half of the stellar rotation period of 73.41 d mentioned in the literature. The behaviour of the mean longitudinal magnetic field is consistent with the assumption of a single-wave variation during the stellar rotation cycle, indicating a dominant dipolar contribution to the magnetic field topology. The estimated polar strength of the surface dipole B-d is larger than 1.15 kG. Further, we compared the behaviour of the line profiles of various elements at different rotation phases associated with different magnetic field strengths. The strongest contribution of the emission component is observed at the phases when the magnetic field shows a negative or positive extremum. The comparison of the spectral behaviour of CPD -28 degrees 2561 with that of another Of?p star, HD 148937 of similar spectral type, reveals remarkable differences in the degree of variability between both stars. Finally, we present new X-ray observations obtained with the Suzaku X-ray Observatory. We report that the star is X-ray bright with log L-X/L-bol approximate to -5.7. The low-resolution X-ray spectra reveal the presence of a plasma heated up to 24 MK. We associate the 24 MK plasma in CPD -28 degrees 2561 with the presence of a kG strong magnetic field capable to confine stellar wind. KW - stars: atmospheres KW - stars: individual: CPD-28 degrees 2561 KW - stars: magnetic field KW - stars: mass-loss KW - stars: variables: general KW - X-rays: stars Y1 - 2015 U6 - https://doi.org/10.1093/mnras/stu2516 SN - 0035-8711 SN - 1365-2966 VL - 447 IS - 2 SP - 1885 EP - 1894 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Toalá, Jesús Alberto A1 - Bowman, Dominic A1 - Van Reeth, Timothy A1 - Todt, Helge Tobias A1 - Dsilva, Karan A1 - Shenar, Tomer A1 - Koenigsberger, Gloria Suzanne A1 - Estrada-Dorado, Sandino A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer T1 - Multiple variability time-scales of the early nitrogen-rich Wolf-Rayet star WR 7 JF - Monthly notices of the Royal Astronomical Society N2 - We present the analysis of the optical variability of the early, nitrogen-rich Wolf-Rayet (WR) star WR 7. The analysis of multisector Transiting Exoplanet Survey Satellite (TESS) light curves and high-resolution spectroscopic observations confirm multiperiodic variability that is modulated on time-scales of years. We detect a dominant period of 2.6433 +/- 0.0005 d in the TESS sectors 33 and 34 light curves in addition to the previously reported high-frequency features from sector 7. We discuss the plausible mechanisms that may be responsible for such variability in WR 7, including pulsations, binarity, co-rotating interaction regions (CIRs), and clumpy winds. Given the lack of strong evidence for the presence of a stellar or compact companion, we suggest that WR 7 may pulsate in quasi-coherent modes in addition to wind variability likely caused by CIRs on top of stochastic low-frequency variability. WR 7 is certainly a worthy target for future monitoring in both spectroscopy and photometry to sample both the short (less than or similar to 1 d) and long (greater than or similar to 1000 d) variability time-scales. KW - stars: atmospheres KW - stars: evolution KW - stars: individual: WR 7 KW - stars: winds KW - outflows KW - stars: Wolft-Rayet Y1 - 2022 U6 - https://doi.org/10.1093/mnras/stac1455 SN - 0035-8711 SN - 1365-2966 VL - 514 IS - 2 SP - 2269 EP - 2277 PB - Oxford University Press CY - Oxford ER - TY - JOUR A1 - Bozzo, Enrico A1 - Bhalerao, V. A1 - Pradhan, Prajal A1 - Tomsick, J. A1 - Romano, Patrizia A1 - Ferrigno, Carlo A1 - Chaty, S. A1 - Oskinova, Lida A1 - Manousakis, A. A1 - Walter, R. A1 - Falanga, M. A1 - Campana, S. A1 - Stella, L. A1 - Ramolla, M. A1 - Chini, R. T1 - Multi-wavelength observations of IGR J17544-2619 from quiescence to outburst JF - Journal of geophysical research : Earth surface N2 - In this paper we report on a long multi-wavelength observational campaign of the supergiant fast X-ray transient prototype IGR J17544-2619. A 150 ks-long observation was carried out simultaneously with XMM-Newton and NuSTAR, catching the source in an initial faint X-ray state and then undergoing a bright X-ray outburst lasting approximately 7 ks. We studied the spectral variability during outburst and quiescence by using a thermal and bulk Comptonization model that is typically adopted to describe the X-ray spectral energy distribution of young pulsars in high mass X-ray binaries. Although the statistics of the collected X-ray data were relatively high, we could neither confirm the presence of a cyclotron line in the broad-band spectrum of the source (0.5-40 keV), nor detect any of the previously reported tentative detections of the source spin period. The monitoring carried out with Swift/XRT during the same orbit of the system observed by XMM-Newton and NuSTAR revealed that the source remained in a low emission state for most of the time, in agreement with the known property of all supergiant fast X-ray transients being significantly sub-luminous compared to other supergiant X-ray binaries. Optical and infrared observations were carried out for a total of a few thousand seconds during the quiescence state of the source detected by XMM-Newton and NuSTAR. The measured optical and infrared magnitudes were slightly lower than previous values reported in the literature, but compatible with the known micro-variability of supergiant stars. UV observations obtained with the UVOT telescope on-board Swift did not reveal significant changes in the magnitude of the source in this energy domain compared to previously reported values. KW - X-rays: binaries Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201629311 SN - 1432-0746 VL - 596 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Oskinova, Lida A1 - Kubatova, Brankica A1 - Hamann, Wolf-Rainer T1 - Moving inhomogeneous envelopes of stars JF - Transport in Porous Media N2 - Massive stars are extremely luminous and drive strong winds, blowing a large part of their matter into the galactic environment before they finally explode as a supernova. Quantitative knowledge of massive star feedback is required to understand our Universe as we see it. Traditionally, massive stars have been studied under the assumption that their winds are homogeneous and stationary, largely relying on the Sobolev approximation. However, Observations with the newest instruments, together with progress in model calculations, ultimately dictate a cardinal change of this paradigm: stellar winds are highly inhomogeneous. Hence, we are now advancing to a new stage in our understanding of stellar winds. Using the foundations laid by V.V. Sobolev and his school, we now update and further develop the stellar spectral analysis techniques. New sophisticated 3-D models of radiation transfer in inhomogeneous expanding media elucidate the physics of stellar winds and improve classical empiric mass-loss rate diagnostics. Applications of these new techniques to multiwavelength observations of massive stars yield consistent and robust stellar wind parameters. (C) 2016 Elsevier Ltd. All rights reserved. KW - Stars: mass-loss KW - Stars: winds KW - Outflows KW - Stars: atmospheres early type Y1 - 2016 U6 - https://doi.org/10.1016/j.jqsrt.2016.06.017 SN - 0022-4073 SN - 1879-1352 VL - 183 SP - 100 EP - 112 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Gimenez-Garcia, Ana A1 - Shenar, Tomer A1 - Torrejon, J. M. A1 - Oskinova, Lida A1 - Martinez-Nunez, S. A1 - Hamann, Wolf-Rainer A1 - Rodes-Roca, J. J. A1 - González-Galan, A. A1 - Alonso-Santiago, J. A1 - González-Fernández, C. A1 - Bernabeu, Guillermo A1 - Sander, Andreas Alexander Christoph T1 - Measuring the stellar wind parameters in IGR J17544-2619 and Vela X-1 constrains the accretion physics in supergiant fast X-ray transient and classical supergiant X-ray binaries JF - Siberian Mathematical Journal N2 - Aims. To close this gap, we perform a comparative analysis of the optical companion in two important systems: IGR J175442619 (SFXT) and Vela X-1 (SGXB). We analyze the spectra of each star in detail and derive their stellar and wind properties. As a next step, we compare the wind parameters, giving us an excellent chance of recognizing key differences between donor winds in SFXTs and SGXBs. Methods. We use archival infrared, optical and ultraviolet observations, and analyze them with the non-local thermodynamic equilibrium (NLTE) Potsdam Wolf-Rayet model atmosphere code. We derive the physical properties of the stars and their stellar winds, accounting for the influence of X-rays on the stellar winds. Results. We find that the stellar parameters derived from the analysis generally agree well with the spectral types of the two donors: O9I (IGR J17544-2619) and B0.5Iae (Vela X-1). The distance to the sources have been revised and also agree well with the estimations already available in the literature. In IGR J17544-2619 we are able to narrow the uncertainty to d = 3.0 +/- 0.2 kpc. From the stellar radius of the donor and its X-ray behavior, the eccentricity of IGR J17544-2619 is constrained to e < 0.25. The derived chemical abundances point to certain mixing during the lifetime of the donors. An important difference between the stellar winds of the two stars is their terminal velocities (v(infinity) = 1500 km s(-1) in IGR J17544-2619 and v(infinity) = 700 km s(-1) in Vela X-1), which have important consequences on the X-ray luminosity of these sources. Conclusions. The donors of IGR J17544-2619 and Vela X-1 have similar spectral types as well as similar parameters that physically characterize them and their spectra. In addition, the orbital parameters of the systems are similar too, with a nearly circular orbit and short orbital period. However, they show moderate differences in their stellar wind velocity and the spin period of their neutron star which has a strong impact on the X-ray luminosity of the sources. This specific combination of wind speed and pulsar spin favors an accretion regime with a persistently high luminosity in Vela X-1, while it favors an inhibiting accretion mechanism in IGR J17544-2619. Our study demonstrates that the relative wind velocity is critical in class determination for the HMXBs hosting a supergiant donor, given that it may shift the accretion mechanism from direct accretion to propeller regimes when combined with other parameters. KW - accretion, accretion disks KW - methods: observational KW - techniques: spectroscopic KW - stars: atmospheres KW - X-rays: binaries KW - stars: winds, outflows Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527551 SN - 1432-0746 VL - 591 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Schoeller, M. A1 - Hubrig, Swetlana A1 - Ilyin, Ilya A1 - Kharchenko, N. V. A1 - Briquet, Maryline A1 - Gonzalez, J. F. A1 - Langer, Norbert A1 - Oskinova, Lida T1 - Magnetic field studies of massive main sequence stars JF - Astronomische Nachrichten = Astronomical notes N2 - We report on the status of our spectropolarimetric observations of massive stars. During the last years, we have discovered magnetic fields in many objects of the upper main sequence, including Be stars, beta Cephei and Slowly Pulsating B stars, and a dozen O stars. Since the effects of those magnetic fields have been found to be substantial by recent models, we are looking into their impact on stellar rotation, pulsation, stellar winds, and chemical abundances. Accurate studies of the age, environment, and kinematic characteristics of the magnetic stars are also promising to give us new insight into the origin of the magnetic fields. Furthermore, longer time series of magnetic field measurements allow us to observe the temporal variability of the magnetic field and to deduce the stellar rotation period and the magnetic field geometry. Studies of the magnetic field in massive stars are indispensable to understand the conditions controlling the presence of those fields and their implications on the stellar physical parameters and evolution. KW - stars: early-type KW - stars: magnetic fields KW - stars: kinematics KW - techniques: polarimetric Y1 - 2011 U6 - https://doi.org/10.1002/asna.201111606 SN - 0004-6337 VL - 332 IS - 9-10 SP - 994 EP - 997 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Surlan, B. A1 - Hamann, Wolf-Rainer A1 - Aret, A. A1 - Kubat, Jiří A1 - Oskinova, Lida A1 - Torres, A. F. T1 - Macroclumping as solution of the discrepancy between Ha and P v mass loss diagnostics for O-type stars JF - ASTRONOMY & ASTROPHYSICS N2 - Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Ha emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims. In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from 04 to 07) and test whether the reported discrepancies can be resolved this way. Methods. In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Ha emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles. Results. Our results show that with the mass-loss rates that fit Ha (and other Balmer and He II lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions. Macroclumping resolves the previously reported discrepancy between Ha and P v mass-loss diagnostics. KW - stars: winds, outflows KW - stars: mass-loss KW - stars: early-type Y1 - 2013 U6 - https://doi.org/10.1051/0004-6361/201322390 SN - 0004-6361 SN - 1432-0746 VL - 559 PB - EDP SCIENCES S A CY - LES ULIS CEDEX A ER - TY - JOUR A1 - Sturm, R. A1 - Haberl, F. A1 - Oskinova, Lida A1 - Schurch, M. P. E. A1 - Henault-Brunet, V. A1 - Gallagher, J. S. A1 - Udalski, A. T1 - Long-term evolution of the neutron-star spin period of SXP1062 JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The Be/X-ray binary SXP 1062 is of especial interest owing to the large spin period of the neutron star, its large spin-down rate, and the association with a supernova remnant constraining its age. This makes the source an important probe for accretion physics. Aims. To investigate the long-term evolution of the spin period and associated spectral variations, we performed an XMM-Newton target-of-opportunity observation of SXP 1062 during X-ray outburst. Methods. Spectral and timing analysis of the XMM-Newton data was compared with previous studies, as well as complementary Swift/XRT monitoring and optical spectroscopy with the SALT telescope were obtained. Results. The spin period was measured to be P-s = (1071.01 +/- 0.16) s on 2012 Oct. 14. The X-ray spectrum is similar to that of previous observations. No convincing cyclotron absorption features, which could be indicative for a high magnetic field strength, are found. The high-resolution RGS spectra indicate the presence of emission lines, which may not completely be accounted for by the SNR emission. The comparison of multi-epoch optical spectra suggest an increasing size or density of the decretion disc around the Be star. Conclusions. SXP 1062 showed a net spin-down with an average of P-s = ( 2.27 +/- 0.44) s yr(-1) over a baseline of 915 days. KW - pulsars: individual: SXP1062 KW - galaxies: individual: Small Magellanic Cloud KW - stars: emission-line, Be KW - stars: neutron KW - X-rays: binaries Y1 - 2013 U6 - https://doi.org/10.1051/0004-6361/201321755 SN - 0004-6361 VL - 556 IS - 4 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Kholtygin, A. F. A1 - Fabrika, S. N. A1 - Rusomarov, N. A1 - Hamann, Wolf-Rainer A1 - Kudryavtsev, D. O. A1 - Oskinova, Lida A1 - Chountonov, G. A. T1 - Line profile variability and magnetic fields of Wolf-Rayet stars: WR 135 and WR 136 JF - ASTRONOMISCHE NACHRICHTEN N2 - We have obtained spectropolarimetric observations of two Wolf-Rayet stars, WR 135 (WC8) and WR 136 (WN6), with the 6-m Russian telescope in July 2009 and July 2010. We have studied the He II 5412 angstrom line region, which contains also the C IV 5469 angstrom line (for WR 135 only). Our goals were to investigate the rapid line-profile variability (LPV) in WR star spectra and to search for magnetic fields. We find small amplitude emission peaks moving from the center of He II line to its wings during the night in spectra of both stars. These emission peaks are likely a signature of accelerating clumps in the stellar wind. We obtained upper limits of the magnetic field strength: approximate to 200G for WR 135 and approximate to 50G for WR 136. (C) 2011 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim KW - stars: atmospheres KW - stars: magnetic fields KW - stars: winds KW - stars: Wolf-Rayet KW - techniques: polarimetric Y1 - 2011 U6 - https://doi.org/10.1002/asna.201111595 SN - 0004-6337 VL - 332 IS - 9-10 SP - 1008 EP - 1011 PB - WILEY-BLACKWELL CY - MALDEN ER - TY - JOUR A1 - Oskinova, Lida A1 - Schaerer, Daniel T1 - Ionization of He II in star-forming galaxies by X-rays from cluster winds and superbubbles JF - Astronomy and astrophysics : an international weekly journal N2 - The nature of the sources powering nebular He II emission in star-forming galaxies remains debated, and various types of objects have been considered, including Wolf-Rayet stars, X-ray binaries, and Population III stars. Modern X-ray observations show the ubiquitous presence of hot gas filling star-forming galaxies. We use a collisional ionization plasma code to compute the specific He II ionizing flux produced by hot gas and show that if its temperature is not too high (less than or similar to 2.5 MK), then the observed levels of soft diffuse X-ray radiation could explain He II ionization in galaxies. To gain a physical understanding of this result, we propose a model that combines the hydrodynamics of cluster winds and hot superbubbles with observed populations of young massive clusters in galaxies. We find that in low-metallicity galaxies, the temperature of hot gas is lower and the production rate of He II ionizing photons is higher compared to high-metallicity galaxies. The reason is that the slower stellar winds of massive stars in lower-metallicity galaxies input less mechanical energy in the ambient medium. Furthermore, we show that ensembles of star clusters up to similar to 10-20 Myr old in galaxies can produce enough soft X-rays to induce nebular He II emission. We discuss observations of the template low-metallicity galaxy I Zw 18 and suggest that the He II nebula in this galaxy is powered by a hot superbubble. Finally, appreciating the complex nature of stellar feedback, we suggest that soft X-rays from hot superbubbles are among the dominant sources of He II ionizing flux in low-metallicity star-forming galaxies. KW - galaxies KW - ISM KW - high-redshift KW - bubbles KW - X-rays Y1 - 2022 U6 - https://doi.org/10.1051/0004-6361/202142520 SN - 0004-6361 SN - 1432-0746 VL - 661 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Ignace, R. A1 - Toalá, Jesús Alberto A1 - Oskinova, Lida T1 - Inversion of Intensity Profiles for Bubble Emissivity JF - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015 N2 - Under the assumption of spherical symmetry, the run of intensity with impact parameter for a spatially resolved and optically thin bubble can be inverted for an "effective emissivity" as a function of radius. The effective emissivity takes into account instrumental sensitivity and even interstellar absorption. This work was supported by a grant from NASA (G03-14008X). Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88432 SP - 358 ER - TY - JOUR A1 - Oskinova, Lida A1 - Bulik, Tomasz A1 - Gomez-Moran, Ada Nebot T1 - Infrared outbursts as potential tracers of common-envelope events in high-mass X-ray binary formation JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Classic massive binary evolutionary scenarios predict that a transitional common-envelope (CE) phase could be preceded as well as succeeded by the evolutionary stage when a binary consists of a compact object and a massive star, that is, a high-mass X-ray binary (HMXB). The observational manifestations of common envelope are poorly constrained. We speculate that its ejection might be observed in some cases as a transient event at mid-infrared (IR) wavelengths. Aims. We estimate the expected numbers of CE ejection events and HMXBs per star formation unit rate, and compare these theoretical estimates with observations. Methods. We compiled a list of 85 mid-IR transients of uncertain nature detected by the Spitzer Infrared Intensive Transients Survey and searched for their associations with X-ray, optical, and UV sources. Results. Confirming our theoretical estimates, we find that only one potential HMXB may be plausibly associated with an IR-transient and tentatively propose that X-ray source NGC4490-X40 could be a precursor to the SPIRITS 16az event. Among other interesting sources, we suggest that the supernova remnant candidate [BWL2012] 063 might be associated with SPIRITS 16ajc. We also find that two SPIRITS events are likely associated with novae, and seven have potential optical counterparts. Conclusions. The massive binary evolutionary scenarios that involve CE events do not contradict currently available observations of IR transients and HMXBs in star-forming galaxies. KW - X-rays: binaries KW - stars: massive KW - infrared: general KW - infrared: galaxies Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201832925 SN - 0004-6361 SN - 1432-0746 VL - 613 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Brown, John C. A1 - Barrett, R. K. A1 - Oskinova, Lida A1 - Owocki, S. P. A1 - Hamann, Wolf-Rainer A1 - de Jong, J. A. A1 - Kaper, L. A1 - Henrichs, H. F. T1 - Inference of hot star density stream properties from data on rotationally recurrent DACs N2 - The information content of data on rotationally periodic recurrent discrete absorption components (DACs) in hot star wind emission lines is discussed. The data comprise optical depths tau(w,phi) as a function of dimensionless Doppler velocity w=(Deltalambda/lambda(0))(c/v(infinity)) and of time expressed in terms of stellar rotation angle phi. This is used to study the spatial distributions of density, radial and rotational velocities, and ionisation structures of the corotating wind streams to which recurrent DACs are conventionally attributed. The simplifying assumptions made to reduce the degrees of freedom in such structure distribution functions to match those in the DAC data are discussed and the problem then posed in terms of a bivariate relationship between tau(w, phi) and the radial velocity v(r)(r), transverse rotation rate Omega(r) and density rho(r, phi) structures of the streams. The discussion applies to cases where: the streams are equatorial; the system is seen edge on; the ionisation structure is approximated as uniform; the radial and transverse velocities are taken to be functions only of radial distance but the stream density is allowed to vary with azimuth. The last kinematic assumption essentially ignores the dynamical feedback of density on velocity and the relationship of this to fully dynamical models is discussed. The case of narrow streams is first considered, noting the result of Hamann et al. (2001) that the apparent acceleration of a narrow stream DAC is higher than the acceleration of the matter itself, so that the apparent slow acceleration of DACs cannot be attributed to the slowness of stellar rotation. Thus DACs either involve matter which accelerates slower than the general wind flow, or they are formed by structures which are not advected with the matter flow but propagate upstream (such as Abbott waves). It is then shown how, in the kinematic model approximation, the radial speed of the absorbing matter can be found by inversion of the apparent acceleration of the narrow DAC, for a given rotation law. The case of broad streams is more complex but also more informative. The observed tau(w,phi) is governed not only by v(r)(r) and Omega(r) of the absorbing stream matter but also by the density profile across the stream, determined by the azimuthal (phi(0)) distribution function F- 0(phi(0)) of mass loss rate around the stellar equator. When F-0(phi(0)) is fairly wide in phi(0), the acceleration of the DAC peak tau(w, phi) in w is generally slow compared with that of a narrow stream DAC and the information on v(r)(r), Omega(r) and F-0(phi(0)) is convoluted in the data tau(w, phi). We show that it is possible, in this kinematic model, to recover by inversion, complete information on all three distribution functions v(r)(r), Omega(r) and F- 0(phi(0)) from data on tau(w, phi) of sufficiently high precision and resolution since v(r)(r) and Omega(r) occur in combination rather than independently in the equations. This is demonstrated for simulated data, including noise effects, and is discussed in relation to real data and to fully hydrodynamic models Y1 - 2004 SN - 0004-6361 ER - TY - CHAP A1 - Feldmeier, Achim A1 - Hamann, Wolf-Rainer A1 - Rätzel, D. A1 - Oskinova, Lida T1 - Hydrodynamic simulations of clumps N2 - Clumps in hot star winds can originate from shock compression due to the line driven instability. One-dimensional hydrodynamic simulations reveal a radial wind structure consisting of highly compressed shells separated by voids, and colliding with fast clouds. Two-dimensional simulations are still largely missing, despite first attempts. Clumpiness dramatically affects the radiative transfer and thus all wind diagnostics in the UV, optical, and in X-rays. The microturbulence approximation applied hitherto is currently superseded by a more sophisticated radiative transfer in stochastic media. Besides clumps, i.e. jumps in the density stratification, so-called kinks in the velocity law, i.e. jumps in dv/dr, play an eminent role in hot star winds. Kinks are a new type of radiative-acoustic shock, and propagate at super-Abbottic speed. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17975 ER - TY - GEN A1 - Oskinova, Lida A1 - Gayley, K. G. A1 - Hamann, Wolf-Rainer A1 - Hünemörder, D. P. A1 - Ignace, R. A1 - Pollock, A. M. T. T1 - High-Resolution X-Ray Spectroscopy reveals the special nature of Wolf-Rayet star winds (pg 747, 2012) T2 - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters Y1 - 2012 U6 - https://doi.org/10.1088/2041-8205/752/2/L35 SN - 2041-8205 VL - 752 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Oskinova, Lida A1 - Gayley, K. G. A1 - Hamann, Wolf-Rainer A1 - Huenemoerder, D. P. A1 - Ignace, R. A1 - Pollock, A. M. T. T1 - HIGH-RESOLUTION X-RAY SPECTROSCOPY REVEALS THE SPECIAL NATURE OF WOLF-RAYET STAR WINDS JF - ASTROPHYSICAL JOURNAL LETTERS N2 - We present the first high-resolutionX-ray spectrum of a putatively singleWolf-Rayet (WR) star. 400 ks observations of WR 6 by the XMM-Newton telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability (LDI) could create shocks. The X-ray emitting plasma reaches temperatures up to 50 MK and is embedded within the unshocked, "cool" stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at approximate to 6.4 keV. The presence of fluorescence is consistent with a two-component medium, where the cool wind is permeated with the hot X-ray emitting plasma. The wind must have a very porous structure to allow the observed amount of X-rays to escape. We find that neither the LDI nor any alternative binary scenario can explain the data. We suggest a scenario where X-rays are produced when the fast wind rams into slow "sticky clumps" that resist acceleration. Our new data show that the X-rays in single WR star are generated by some special mechanism different from the one operating in the O-star winds. KW - stars: individual (WR 6) KW - stars: winds, outflows KW - stars: Wolf-Rayet KW - X-rays: stars Y1 - 2012 U6 - https://doi.org/10.1088/2041-8205/747/2/L25 SN - 2041-8205 VL - 747 IS - 2 PB - IOP PUBLISHING LTD CY - BRISTOL ER - TY - JOUR A1 - Oskinova, Lida A1 - Feldmeier, Achim A1 - Hamann, Wolf-Rainer T1 - High-resolution X-ray spectroscopy of bright O-type stars JF - Monthly notices of the Royal Astronomical Society N2 - Archival X-ray spectra of the four prominent single, non-magnetic O stars zeta Pup, zeta Ori, xi Per and zeta Oph, obtained in high resolution with Chandra HETGS/MEG have been studied. The resolved X-ray emission line profiles provide information about the shocked, hot gas which emits the X-radiation, and about the bulk of comparably cool stellar wind material which partly absorbs this radiation. In this paper, we synthesize X-ray line profiles with a model of a clumpy stellar wind. We find that the geometrical shape of the wind inhomogeneities is important: better agreement with the observations can be achieved with radially compressed clumps than with spherical clumps. The parameters of the model, i.e. chemical abundances, stellar radius, mass-loss rate and terminal wind velocity, are taken from existing analyses of UV and optical spectra of the programme stars. On this basis, we also calculate the continuum-absorption coefficient of the cool-wind material, using the Potsdam Wolf-Rayet (POWR) model atmosphere code. The radial location of X-ray emitting gas is restricted from analysing the FIR line ratios of helium-like ions. The only remaining free parameter of our model is the typical distance between the clumps; here, we assume that at any point in the wind there is one clump passing by per one dynamical time-scale of the wind. The total emission in a model line is scaled to the observation. There is a good agreement between synthetic and observed line profiles. We conclude that the X-ray emission line profiles in O stars can be explained by hot plasma embedded in a cool wind which is highly clumped in the form of radially compressed shell fragments. KW - stars : individual : zeta Pup KW - stars : individual : zeta Ori KW - stars : individual : xi Per KW - stars : individual : zeta Oph KW - X-rays : stars Y1 - 2006 U6 - https://doi.org/10.1111/j.1365-2966.2006.10858.x SN - 0035-8711 VL - 372 SP - 313 EP - 326 PB - Oxford University Press CY - Oxford ER - TY - JOUR A1 - Huenemoerder, D. A1 - Gayley, K. A1 - Hamann, Wolf-Rainer A1 - Ignace, R. A1 - Nichols, J. A1 - Oskinova, Lida A1 - Pollock, A. M. T. A1 - Schulz, N. T1 - High Resolution X-Ray Spectra of WR 6 JF - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015 N2 - As WR 6 is a putatively single WN4 star, and is relatively bright (V = 6.9), it is an ideal case for studying the wind mechanisms in these extremely luminous stars. To obtain higher resolution spectra at higher energy (above 1 keV) than previously obtained with the XMM/Newton RGS, we have observed WR 6 with the Chandra High Energy Transmission Grating Spectrometer for 450 ks. We have resolved emission lines of S, Si, Mg, Ne, and Fe, which all show a “fin"-shaped prole, characteristic of a self-absorbed uniformly expanding shell. Steep blue edges gives robust maximal expansion velocities of about 2000 km/s, somewhat larger than the 1700km/s derived from UV lines. The He-like lines all indicate that X-ray emitting plasmas are far from the photosphere – even at the higher energies where opacity is lowest { as was also the case for the longer wavelength lines observed with XMM-Newton/RGS. Abundances determined from X-ray spectral modeling indicate enhancements consistent with nucleosynthesis. The star was also variable in X-rays and in simultaneous optical photometry obtained with Chandra aspect camera, but not coherently with the optically known period of 3.765 days. Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88236 SP - 301 EP - 304 ER - TY - JOUR A1 - Shrader, C. R. A1 - Hamaguchi, K. A1 - Sturner, S. J. A1 - Oskinova, Lida A1 - Almeyda, T. A1 - Petre, R. T1 - Hifg-energy properties of the enigmatic be STAR gamma Cassiopeiae JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present the results of a broadband X-ray study of the enigmatic Be star Gamma Cassiopeiae (herein gamma Cas) based on observations made with both the Suzaku and INTEGRAL observatories.. Cas has long been recognized as the prototypical example of a small subclass of Be stars with moderately strong X-ray emission dominated by a hot thermal component in the 0.5-12 keV energy range (L-x approximate to 10(32)-10(33) erg s(-1)). This places them at the high end of the known luminosity distribution for stellar emission, but several orders of magnitude below typical accretion-powered Be X-ray binaries. The INTEGRAL observations spanned an eight-year baseline and represent the deepest measurement to date at energies above similar to 50 keV. We find that the INTEGRAL data are consistent within statistics to a constant intensity source above 20 keV, with emission extending up to similar to 100 keV, and that searches for all of the previously reported periodicities of the system at lower energies led to null results. We further find that our combined Suzaku and INTEGRAL spectrum, which we suggest is the most accurate broadband X-ray measurement of gamma Cas to date, is fitted extremely well with a thermal plasma emission model with a single absorption component. We found no compelling need for an additional non-thermal high-energy component. We discuss these results in the context of a currently favored models for gamma Cas and its analogs. KW - gamma rays: stars KW - stars: emission-line, Be KW - stars: individual (gamma Cassiopeiae) KW - white dwarfs KW - X-rays: binaries KW - X-rays: stars Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/799/1/84 SN - 0004-637X SN - 1538-4357 VL - 799 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Naze, Y. A1 - Broos, Patrick S. A1 - Oskinova, Lida A1 - Townsley, L. K. A1 - Cohen, David H. A1 - Corcoran, M. F. A1 - Evans, N. R. A1 - Gagne, M. A1 - Moffat, Anthony F. J. A1 - Pittard, J. M. A1 - Rauw, G. A1 - Ud-Doula, A. A1 - Walborn, N. R. T1 - GLOBAL X-RAY PROPERTIES OF THE O AND B STARS IN CARINA JF - ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES N2 - The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the L-X-L-BOL ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(L-X/L-BOL) is -7.26 for single objects, with a dispersion of only 0.21 dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the L-X-L-BOL ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the L-X-L-BOL ratio in the medium (1.0-2.5 keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared with "normal" O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest among these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes. KW - ISM: individual objects (Carina nebula) KW - stars: massive KW - X-rays: stars Y1 - 2011 U6 - https://doi.org/10.1088/0067-0049/194/1/7 SN - 0067-0049 VL - 194 IS - 1 PB - IOP PUBLISHING LTD CY - BRISTOL ER - TY - JOUR A1 - Hubrig, Swetlana A1 - Oskinova, Lida A1 - Schoeller, M. T1 - First detection of a magnetic field in the fast rotating runaway Oe star zeta Ophiuchi JF - Astronomische Nachrichten = Astronomical notes N2 - The star zeta Ophiuchi is one of the brightest massive stars in the northern hemisphere and was intensively studied in various wavelength domains. The currently available observational material suggests that certain observed phenomena are related to the presence of a magnetic field. We acquired spectropolarimetric observations of zeta Oph with FORS 1 mounted on the 8-m Kueyen telescope of the VLT to investigate if a magnetic field is indeed present in this star. Using all available absorption lines, we detect a mean longitudinal magnetic field < B(z)>(all) = 141 +/- 45 G, confirming the magnetic nature of this star. We review the X-ray properties of zeta Oph with the aim to understand whether the X-ray emission of zeta Oph is dominated by magnetic or by wind instability processes. KW - stars: mass-loss KW - stars: early-type KW - stars: magnetic field KW - stars: kinematics and dynamics KW - X-rays: stars KW - stars: individual: zeta Ophiuchi Y1 - 2011 U6 - https://doi.org/10.1002/asna.201111516 SN - 0004-6337 VL - 332 IS - 2 SP - 147 EP - 152 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Hubrig, Swetlana A1 - Schoeller, M. A1 - Ilyin, Ilya A1 - Kharchenko, N. V. A1 - Oskinova, Lida A1 - Langer, N. A1 - Gonzalez, J. F. A1 - Kholtygin, A. F. A1 - Briquet, Maryline T1 - Exploring the origin of magnetic fields in massive stars - II. New magnetic field measurements in cluster and field stars JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Theories on the origin of magnetic fields in massive stars remain poorly developed, because the properties of their magnetic field as function of stellar parameters could not yet be investigated. Additional observations are of utmost importance to constrain the conditions that are conducive to magnetic fields and to determine first trends about their occurrence rate and field strength distribution. Aims. To investigate whether magnetic fields in massive stars are ubiquitous or appear only in stars with a specific spectral classification, certain ages, or in a special environment, we acquired 67 new spectropolarimetric observations for 30 massive stars. Among the observed sample, roughly one third of the stars are probable members of clusters at different ages, whereas the remaining stars are field stars not known to belong to any cluster or association. Methods. Spectropolarimetric observations were obtained during four different nights using the low-resolution spectropolarimetric mode of FOcal Reducer low dispersion Spectrograph (FORS 2) mounted on the 8-m Antu telescope of the VLT. Furthermore, we present a number of follow-up observations carried out with the high-resolution spectropolarimeters SOFIN mounted at the Nordic Optical Telescope (NOT) and HARPS mounted at the ESO 3.6 m between 2008 and 2011. To assess the membership in open clusters and associations, we used astrometric catalogues with the highest quality kinematic and photometric data currently available. Results. The presence of a magnetic field is confirmed in nine stars previously observed with FORS 1/2: HD36879, HD47839, CPD-28 2561, CPD-47 2963, HD93843, HD148937, HD149757, HD328856, and HD164794. New magnetic field detections at a significance level of at least 3 sigma were achieved in five stars: HD92206c, HD93521, HD93632, CPD-46 8221, and HD157857. Among the stars with a detected magnetic field, five stars belong to open clusters with high membership probability. According to previous kinematic studies, five magnetic O-type stars in our sample are candidate runaway stars. KW - polarization KW - stars: early-type KW - stars: kinematics and dynamics KW - stars: magnetic field KW - stars: massive KW - open clusters and associations: general Y1 - 2013 U6 - https://doi.org/10.1051/0004-6361/201220721 SN - 0004-6361 VL - 551 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Fang, X. A1 - Guerrero, Martín A. A1 - Marquez-Lugo, R. A. A1 - Toala, Jesús Alberto A1 - Arthur, S. J. A1 - Chu, Y.-H. A1 - Blair, William P. A1 - Gruendl, R. A. A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Todt, Helge Tobias T1 - Expansion of hydrogen-poor knots in the born-again planetary nebulae A30 and A78 JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We analyze the expansion of hydrogen-poor knots and filaments in the born-again planetary nebulae A30 and A78 based on Hubble Space Telescope ( HST) images obtained almost 20 yr apart. The proper motion of these features generally increases with distance to the central star, but the fractional expansion decreases, i.e., the expansion is not homologous. As a result, there is not a unique expansion age, which is estimated to be 610-950 yr for A30 and 600-1140 yr for A78. The knots and filaments have experienced complex dynamical processes: the current fast stellar wind is mass loaded by the material ablated from the inner knots; the ablated material is then swept up until it shocks the inner edges of the outer, hydrogen-rich nebula. The angular expansion of the outer filaments shows a clear dependence on position angle, indicating that the interaction of the stellar wind with the innermost knots channels the wind along preferred directions. The apparent angular expansion of the innermost knots seems to be dominated by the rocket effect of evaporating gas and by the propagation of the ionization front inside them. Radiation-hydrodynamical simulations show that a single ejection of material followed by a rapid onset of the stellar wind and ionizing flux can reproduce the variety of clumps and filaments at different distances from the central star found in A30 and A78. KW - ISM: kinematics and dynamics KW - planetary nebulae: individual (A30 and A78) Y1 - 2014 U6 - https://doi.org/10.1088/0004-637X/797/2/100 SN - 0004-637X SN - 1538-4357 VL - 797 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Oskinova, Lida T1 - Evolution of X-ray emission from young massive star clusters N2 - The evolution of X-ray emission from young massive star clusters is modelled, taking into account the emission from the stars as well as from the cluster wind. It is shown that the level and character of the soft (0.2-10 keV) X-ray emission change drastically with cluster age and are tightly linked with stellar evolution. Using the modem X-ray observations of massive stars, we show that the correlation between bolometric and X-ray luminosity known for single O stars also holds for O + O and (Wolf-Rayet) WR + O binaries. The diffuse emission originates from the cluster wind heated by the kinetic energy of stellar winds and supernova explosions. To model the evolution of the cluster wind, the mass and energy yields from a population synthesis are used as input to a hydrodynamic model. It is shown that in a very young cluster the emission from the cluster wind is low. When the cluster evolves, WR stars are formed. Their strong stellar winds power an increasing X-ray emission of the cluster wind. Subsequent supernova explosions pump the level of diffuse emission even higher. Clusters at this evolutionary stage may have no X-ray-bright stellar point sources, but a relatively high level of diffuse emission. A supernova remnant may become a dominant X-ray source, but only for a short time interval of a few thousand years. We retrieve and analyse Chandra and XMM-Newton observations of six massive star clusters located in the Large Magellanic Cloud (LMC). Our model reproduces the observed diffuse and point-source emission from these LMC clusters, as well as from the Galactic clusters Arches, Quintuplet and NGC 3603 Y1 - 2005 SN - 0035-8711 ER - TY - JOUR A1 - Oskinova, Lida A1 - Todt, Helge Tobias A1 - Ignace, Richard A1 - Brown, John C. A1 - Cassinelli, Joseph P. A1 - Hamann, Wolf-Rainer T1 - Early magnetic B-type stars X-ray emission and wind properties JF - Monthly notices of the Royal Astronomical Society N2 - We present a comprehensive study of X-ray emission by, and wind properties of, massive magnetic early B-type stars. Dedicated XMM-Newton observations were obtained for three early-type B-type stars, xi(1) CMa, V2052 Oph and zeta Cas, with recently discovered magnetic fields. We report the first detection of X-ray emission from V2052 Oph and zeta Cas. The latter is one the softest X-ray sources among the early-type stars, while the former is one of the X-ray faintest. The observations show that the X-ray spectra of our programme stars are quite soft with the bulk of X-ray emitting material having a temperature of about 1 MK. We compile the complete sample of early B-type stars with detected magnetic fields to date and existing X-ray measurements, in order to study whether the X-ray emission can be used as a general proxy for stellar magnetism. We find that the X-ray properties of early massive B-type magnetic stars are diverse, and that hard and strong X-ray emission does not necessarily correlate with the presence of a magnetic field, corroborating similar conclusions reached earlier for the classical chemically peculiar magnetic Bp-Ap stars. We analyse the ultraviolet (UV) spectra of five non-supergiant B stars with magnetic fields (tau Sco, beta Cep, xi(1) CMa, V2052 Oph and zeta Cas) by means of non-local thermodynamic equilibrium (non-LTE) iron-blanketed model atmospheres. The latter are calculated with the Potsdam Wolf-Rayet (PoWR) code, which treats the photosphere as well as the wind, and also accounts for X-rays. With the exception of t Sco, this is the first analysis of these stars by means of stellar wind models. Our models accurately fit the stellar photospheric spectra in the optical and the UV. The parameters of X-ray emission, temperature and flux are included in the model in accordance with observations. We confirm the earlier findings that the filling factors of X-ray emitting material are very high. Our analysis reveals that the magnetic early-type B stars studied here have weak winds with velocities not significantly exceeding upsilon(esc). The mass-loss rates inferred from the analysis of UV lines are significantly lower than predicted by hydrodynamically consistent models. We find that, although the X-rays strongly affect the ionization structure of the wind, this effect is not sufficient in reducing the total radiative acceleration. When the X-rays are accounted for at the intensity and temperatures observed, there is still sufficient radiative acceleration to drive a stronger mass-loss than we empirically infer from the UV spectral lines. KW - techniques: spectroscopic KW - stars: magnetic field KW - stars: massive KW - stars: mass loss KW - X-rays: stars Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2966.2011.19143.x SN - 0035-8711 VL - 416 IS - 2 SP - 1456 EP - 1474 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Oskinova, Lida A1 - Naze, Yael A1 - Todt, Helge Tobias A1 - Huenemoerder, David P. A1 - Ignace, Richard A1 - Hubrig, Swetlana A1 - Hamann, Wolf-Rainer T1 - Discovery of X-ray pulsations from a massive star JF - Nature Communications N2 - X-ray emission from stars much more massive than the Sun was discovered only 35 years ago. Such stars drive fast stellar winds where shocks can develop, and it is commonly assumed that the X-rays emerge from the shock-heated plasma. Many massive stars additionally pulsate. However, hitherto it was neither theoretically predicted nor observed that these pulsations would affect their X-ray emission. All X-ray pulsars known so far are associated with degenerate objects, either neutron stars or white dwarfs. Here we report the discovery of pulsating X-rays from a non-degenerate object, the massive B-type star xi(1) CMa. This star is a variable of beta Cep-type and has a strong magnetic field. Our observations with the X-ray Multi-Mirror (XMM-Newton) telescope reveal X-ray pulsations with the same period as the fundamental stellar oscillations. This discovery challenges our understanding of stellar winds from massive stars, their X-ray emission and their magnetism. Y1 - 2014 U6 - https://doi.org/10.1038/ncomms5024 SN - 2041-1723 VL - 5 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Oskinova, Lida A1 - Sun, W. A1 - Evans, C. J. A1 - Henault-Brunet, V. A1 - Chu, Y.-H. A1 - Gallagher, J. S. A1 - Guerrero, Martín A. A1 - Gruendl, R. A. A1 - Güdel, M. A1 - Silich, S. A1 - Chen, Y. A1 - Naze, Y. A1 - Hainich, Rainer A1 - Reyes-Iturbide, J. T1 - Discovery of x-ray emission from young suns in the small magellanic cloud JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We report the discovery of extended X-ray emission within the young star cluster NGC 602a in the Wing of the Small Magellanic Cloud (SMC) based on observations obtained with the Chandra X-Ray Observatory. X-ray emission is detected from the cluster core area with the highest stellar density and from a dusty ridge surrounding the H II region. We use a census of massive stars in the cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to provide a significant contribution to the X-ray emission detected from the central area of the cluster. We therefore suggest that X-ray emission at the cluster core originates from an ensemble of low-and solar-mass pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be detected individually. We attribute the X-ray emission from the dusty ridge to the embedded tight cluster of the newborn stars known in this area from infrared studies. Assuming that the levels of X-ray activity in young stars in the low-metallicity environment of NGC 602a are comparable to their Galactic counterparts, then the detected spatial distribution, spectral properties, and level of X-ray emission are largely consistent with those expected from low-and solar-mass PMS stars and young stellar objects (YSOs). This is the first discovery of X-ray emission attributable to PMS stars and YSOs in the SMC, which suggests that the accretion and dynamo processes in young, low-mass objects in the SMC resemble those in the Galaxy. KW - Magellanic Clouds KW - ISM: bubbles KW - H II regions KW - stars: winds, outflows KW - stars: pre-main sequence KW - X-rays: stars Y1 - 2013 U6 - https://doi.org/10.1088/0004-637X/765/1/73 SN - 0004-637X VL - 765 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Feldmeier, Achim A1 - Ignace, Richard A1 - Chu, You-Hua T1 - Discovery of X-ray emission from the Wolf-Rayet star WR 142 of oxygen subtype N2 - We report the discovery of weak yet hard X-ray emission from the Wolf-Rayet (WR) star WR 142 with the XMM- Newton X-ray telescope. Being of spectral subtype WO2, WR 142 is a massive star in a very advanced evolutionary stage shortly before its explosion as a supernova or. gamma-ray burst. This is the first detection of X-ray emission from a WO- type star. We rule out any serendipitous X-ray sources within approximate to 1 '' of WR 142. WR 142 has an X- ray luminosity of L-X approximate to 7 x 10(30) erg s(-1), which constitutes only less than or similar to 10(-8) of its bolometric luminosity. The hard X-ray spectrum suggests a plasma temperature of about 100 MK. Commonly, X-ray emission from stellar winds is attributed to embedded shocks due to the intrinsic instability of the radiation driving. From qualitative considerations we conclude that this mechanism cannot account for the hardness of the observed radiation. There are no hints for a binary companion. Therefore the only remaining, albeit speculative explanation must refer to magnetic activity. Possibly related, WR 142 seems to rotate extremely fast, as indicated by the unusually round profiles of its optical emission lines. Our detection implies that the wind of WR 142 must be relatively transparent to X-rays, which can be due to strong wind ionization, wind clumping, or nonspherical geometry from rapid rotation. Y1 - 2009 UR - http://iopscience.iop.org/0004-637X/ U6 - https://doi.org/10.1088/0004-637x/693/1/L44 SN - 0004-637X ER - TY - JOUR A1 - Hamaguchi, K. A1 - Oskinova, Lida A1 - Russell, C. M. P. A1 - Petre, R. A1 - Enoto, T. A1 - Morihana, K. A1 - Ishida, M. T1 - DISCOVERY OF RAPIDLY MOVING PARTIAL X-RAY ABSORBERS WITHIN GAMMA CASSIOPEIAE JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - detected six rapid X-ray spectral hardening events called "softness dips" in a similar to 100 ks observation in 2011. All the softness dip events show symmetric softness-ratio variations, and some of them have flat bottoms apparently due to saturation. The softness dip spectra are best described by either similar to 40% or similar to 70% partial covering absorption to kT similar to 12 keV plasma emission by matter with a neutral hydrogen column density of similar to(2-8) x 10(21) cm(-2), while the spectrum outside these dips is almost free of absorption. This result suggests the presence of two distinct X-ray-emitting spots in the.. Cas system, perhaps on a white dwarf (WD) companion with dipole mass accretion. The partial covering absorbers may be blobs in the Be stellar wind, the Be disk, or rotating around the WD companion. Weak correlations of the softness ratios to the hard X-ray flux suggest the presence of stable plasmas at kT similar to 0.9 and 5 keV, which may originate from the Be or WD winds. The formation of a Be star and WD binary system requires mass transfer between two stars; gamma Cas may have experienced such activity in the past. KW - blue stragglers KW - stars: emission-line, Be KW - stars: individual (gamma Cassiopeiae) KW - stars: winds, outflows KW - white dwarfs KW - X-rays: stars Y1 - 2016 U6 - https://doi.org/10.3847/0004-637X/832/2/140 SN - 0004-637X SN - 1538-4357 VL - 832 SP - 33 EP - 49 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Ramachandran, Varsha A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer T1 - Discovery of O stars in the tidal Magellanic Bridge BT - Stellar parameters, abundances, and feedback of the nearest metal-poor massive stars and their implication for the Magellanic System ecology JF - Astronomy and astrophysics : an international weekly journal / European Southern Observatory (ESO). Section: Galactic structure, stellar clusters and populations N2 - The Magellanic Bridge, stretching between the Small and the Large Magellanic Cloud (SMC and LMC), is the nearest tidally stripped intergalactic environment. The Bridge has a significantly low average metallicity of Z less than or similar to 0.1 Z(circle dot). Here we report the first discovery of O-type stars in the Magellanic Bridge. Three massive O stars were identified thanks to the archival spectra obtained by the ESO's Very Large Telescope FLAMES instrument. We analyze the spectra of each star using the Potsdam Wolf-Rayet (PoWR) non-local thermodynamic equilibrium model atmosphere code, which provides the physical parameters, ionizing photon fluxes, and surface abundances. The ages of the newly discovered O stars suggest that star formation in the Bridge is ongoing. Furthermore, the discovery of O stars in the Bridge implies that tidally stripped galactic tails containing low-density but highly dynamical gas are capable of producing massive O stars. The multi-epoch spectra indicate that all three O stars are binaries. Despite their spatial proximity to one another, these O stars are chemically distinct. One of them is a fast-rotating giant with nearly LMC-like abundances. The other two are main-sequence stars that rotate extremely slowly and are strongly metal depleted. We discover the most nitrogen-poor O star known to date. Taking into account the previous analyses of B stars in the Bridge, we interpret the various metal abundances as the signature of a chemically inhomogeneous interstellar medium (ISM), suggesting that the Bridge gas might have accreted during multiple episodes of tidal interaction between the Clouds. Attributing the lowest derived metal content to the primordial gas, the time of the initial formation of the Bridge may date back several billion years. Using the Gaia and Galex color-magnitude diagrams, we roughly estimate the total number of O stars in the Bridge and their total ionizing radiation. Comparing this with the energetics of the diffuse ISM, we find that the contribution of the hot stars to the ionizing radiation field in the Bridge is less than 10% and conclude that the main sources of ionizing photons are leaks from the LMC and SMC. We estimate a lower limit for the fraction of ionizing radiation that escapes from these two dwarf galaxies. KW - stars: massive KW - stars: fundamental parameters KW - stars: abundances KW - Magellanic Clouds KW - techniques: spectroscopic KW - stars: atmospheres Y1 - 2021 U6 - https://doi.org/10.1051/0004-6361/202039486 SN - 1432-0746 SN - 0004-6361 VL - 646 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Gvaramadze, V. V. A1 - Kniazev, Alexei Y. A1 - Oskinova, Lida T1 - Discovery of a putative supernova remnant around the long-period X-ray pulsar SXP 1323 in the Small Magellanic Cloud JF - Monthly notices of the Royal Astronomical Society N2 - We report the discovery of a circular shell centred on the Be X-ray binary (BeXB) SXP 1323 in the Small Magellanic Cloud. The shell was detected in an H α image obtained with the Very Large Telescope. Follow-up spectroscopy with the Southern African Large Telescope showed that the shell expands with a velocity of ≈100kms−1 and that its emission is due to shock excitation. We suggest that this shell is a remnant of the supernova explosion that led to the formation of SXP 1323’s neutron star ≈40000 yr ago. SXP 1323 represents the second known case of a BeXB associated with a supernova remnant (the first one is SXP 1062). Interestingly, both of these BeXBs harbour long-period pulsars and are located in a low-metallicity galaxy. KW - stars: emission-line, Be KW - stars: individual: [MA93] 1393 KW - stars: massive KW - ISM: supernova remnants KW - X-rays: binaries KW - X-rays: individual: SXP 1323 Y1 - 2019 U6 - https://doi.org/10.1093/mnrasl/slz018 SN - 0035-8711 SN - 1365-2966 VL - 485 IS - 1 SP - L6 EP - L10 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Gvaramadze, Vasily V. A1 - Fabrika, Sergei Nikolaevich A1 - Hamann, Wolf-Rainer A1 - Sholukhova, Olga N. A1 - Valeev, Azamat F. A1 - Goranskij, Vitaly P. A1 - Cherepashchuk, Anatol M. A1 - Bomans, Dominik J. A1 - Oskinova, Lida T1 - Discovery of a new Wolf-Rayet star and its ring nebula in Cygnus N2 - We report the serendipitous discovery of a ring nebula around a candidate Wolf-Rayet (WR) star, HBHA 4202-22, in Cygnus using the Spitzer Space Telescope archival data. Our spectroscopic follow-up observations confirmed the WR nature of this star (we named it WR 138a) and showed that it belongs to the WN8-9h subtype. We thereby add a new example to the known sample of late WN stars with circumstellar nebulae. We analysed the spectrum of WR 138a by using the Potsdam Wolf-Rayet (PoWR) model atmospheres, obtaining a stellar temperature of 40 kK. The stellar wind composition is dominated by helium with 20 per cent of hydrogen. The stellar spectrum is highly reddened and absorbed (EB- V = 2.4 mag, A(V) = 7.4 mag). Adopting a stellar luminosity of log L/L-circle dot = 5.3, the star has a mass-loss rate of 10-4.7 M- circle dot yr-1, and resides in a distance of 4.2 kpc. We measured the proper motion for WR 138a and found that it is a runaway star with a peculiar velocity of similar or equal to 50 km s-1. Implications of the runaway nature of WR 138a for constraining the mass of its progenitor star and understanding the origin of its ring nebula are discussed. Y1 - 2009 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0035-8711 U6 - https://doi.org/10.1111/j.1365-2966.2009.15492.x SN - 0035-8711 ER - TY - JOUR A1 - Henault-Brunet, V. A1 - Oskinova, Lida A1 - Guerrero, Martín A. A1 - Sun, W. A1 - Chu, Y.-H. A1 - Evans, C. J. A1 - Gallagher, J. S. A1 - Gruendl, R. A. A1 - Reyes-Iturbide, J. T1 - Discovery of a Be/X-ray pulsar binary and associated supernova remnant in the wing of the small magellanic cloud JF - Monthly notices of the Royal Astronomical Society N2 - We report on a new Be/X-ray pulsar binary located in the Wing of the Small Magellanic Cloud (SMC). The strong pulsed X-ray source was discovered with the Chandra and XMM-Newton X-ray observatories. The X-ray pulse period of 1062 s is consistently determined from both Chandra and XMM-Newton observations, revealing one of the slowest rotating X-ray pulsars known in the SMC. The optical counterpart of the X-ray source is the emission-line star 2dFS 3831. Its B0-0.5(III)e+ spectral type is determined from VLT-FLAMES and 2dF optical spectroscopy, establishing the system as a Be/X-ray binary (Be-XRB). The hard X-ray spectrum is well fitted by a power law with additional thermal and blackbody components, the latter reminiscent of persistent Be-XRBs. This system is the first evidence of a recent supernova in the low-density surroundings of NGC602. We detect a shell nebula around 2dFS 3831 in H alpha and [OIII] images and conclude that it is most likely a supernova remnant. If it is linked to the supernova explosion that created this new X-ray pulsar, its kinematic age of (2-4) x 10(4) yr provides a constraint on the age of the pulsar. KW - stars: emission-line, Be KW - ISM: supernova remnants KW - Magellanic Clouds KW - X-rays: binaries Y1 - 2012 U6 - https://doi.org/10.1111/j.1745-3933.2011.01183.x SN - 0035-8711 VL - 420 IS - 1 SP - L13 EP - L17 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Sander, Andreas Alexander Christoph A1 - Fürst, F. A1 - Kretschmar, P. A1 - Oskinova, Lida A1 - Todt, Helge Tobias A1 - Hainich, Rainer A1 - Shenar, Tomer A1 - Hamann, Wolf-Rainer T1 - Coupling hydrodynamics with comoving frame radiative transfer BT - Stellar wind stratification in the high-mass X-ray binary Vela X-1 JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. To gain a realistic picture of the donor star in Vela X-1, we constructed a hydrodynamically consistent atmosphere model describing the wind stratification while properly reproducing the observed donor spectrum. To investigate how X-ray illumination affects the stellar wind, we calculated additional models for different X-ray luminosity regimes. Methods. We used the recently updated version of the Potsdam Wolf-Rayet code to consistently solve the hydrodynamic equation together with the statistical equations and the radiative transfer. Results. The wind flow in Vela X-1 is driven by ions from various elements, with Fe III and S III leading in the outer wind. The model-predicted mass-loss rate is in line with earlier empirical studies. The mass-loss rate is almost unaffected by the presence of the accreting NS in the wind. The terminal wind velocity is confirmed at u(infinity) approximate to 600 km s(-1). On the other hand, the wind velocity in the inner region where the NS is located is only approximate to 100 km s(-1), which is not expected on the basis of a standard beta-velocity law. In models with an enhanced level of X-rays, the velocity field in the outer wind can be altered. If the X-ray flux is too high, the acceleration breaks down because the ionization increases. Conclusions. Accounting for radiation hydrodynamics, our Vela X-1 donor atmosphere model reveals a low wind speed at the NS location, and it provides quantitative information on wind driving in this important HMXB. KW - stars: mass-loss KW - stars: winds, outflows KW - stars: early-type KW - stars: atmospheres KW - stars: massive KW - X-rays: binaries Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201731575 SN - 1432-0746 VL - 610 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Massa, Derck A1 - Oskinova, Lida A1 - Prinja, Raman A1 - Ignace, Richard T1 - Coordinated UV and X-Ray Spectroscopic Observations of the O-type Giant xi Per BT - the Connection between X-Rays and Large-scale Wind Structure JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present new, contemporaneous Hubble Space Telescope STIS and XMM-Newton observations of the O7. III(n) ((f)) star xi Per. We supplement the new data with archival IUE spectra, to analyze the variability of the wind lines and X-ray flux of xi Per. The variable wind of this star is known to have a 2.086-day periodicity. We use a simple, heuristic spot model that fits the low-velocity (near-surface) IUE wind line variability very well, to demonstrate that the low-velocity absorption in the new STIS spectra of N IV lambda 1718 and Si IV lambda 1402 vary with the same 2.086-day period. It is remarkable that the period and amplitude of the STIS data agree with those of the IUE spectra obtained 22 yr earlier. We also show that the time variability of the new XMM-Newton fluxes is also consistent with the 2.086-day period. Thus, our new, multiwavelength coordinated observations demonstrate that the mechanism that causes the UV wind line variability is also responsible for a significant fraction of the X-rays in single O stars. The sequence of events for the multiwavelength light-curve minima is Si IV lambda 1402, N IV lambda 1718, and X-ray flux, each separated by a phase of about 0.06 relative to the 2.086-day period. Analysis of the X-ray fluxes shows that they become softer as they weaken. This is contrary to expectations if the variability is caused by periodic excess absorption. Furthermore, the high-resolution X-ray spectra suggest that the individual emission lines at maximum are more strongly blueshifted. If we interpret the low-velocity wind line light curves in terms of our model, it implies that there are two bright regions, i.e., regions with less absorption, separated by 180 degrees, on the surface of the star. We note that the presence and persistence of two spots separated by 180 degrees suggest that a weak dipole magnetic field is responsible for the variability of the UV wind line absorption and X-ray flux in xi Per. KW - stars: activity KW - stars: early-type KW - stars: winds, outflows KW - ultraviolet: stars KW - X-rays: stars Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/ab0283 SN - 0004-637X SN - 1538-4357 VL - 873 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Shenar, Tomer A1 - Oskinova, Lida A1 - Jaervinen, S. P. A1 - Luckas, P. A1 - Hainich, Rainer A1 - Todt, Helge Tobias A1 - Hubrig, Swetlana A1 - Sander, Andreas Alexander Christoph A1 - Ilyin, Ilya A1 - Hamann, Wolf-Rainer T1 - Constraining the weak-wind problem BT - an XMM-HST campaign for the magnetic 09.7 V star HD 54879 JF - Contributions Of The Astronomical Observatory Skalnate Pleso N2 - Mass-loss rates of massive, late type main sequence stars are much weaker than currently predicted, but their true values are very difficult to measure. We suggest that confined stellar winds of magnetic stars can be exploited to constrain the true mass-loss rates M of massive main sequence stars. We acquired UV, X-ray, and optical amateur data of HD 54879 (09.7 V), one of a few O-type stars with a detected atmospheric magnetic field (B-d greater than or similar to 2 kG). We analyze these data with the Potsdam Wolf-Rayet (PoWR) and XSPEC codes. We can roughly estimate the mass-loss rate the star would have in the absence of a magnetic field as log M-B=0 approximate to -9.0 M-circle dot yr(-1). Since the wind is partially trapped within the Alfven radius rA greater than or similar to 12 R-*,, the true mass-loss rate of HD 54879 is log M less than or similar to -10.2 M-circle dot yr(-1). Moreover, we find that the microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (< 4 km s(-1)). An initial mass of 16 M-circle dot and an age of 5 Myr are inferred. We derive a mean X-ray emitting temperature of log T-x = 6.7 K and an X-ray luminosity of log L-x = 32 erg s(-1). The latter implies a significant X-ray excess (log L-x/L-Bol approximate to - 6.0), most likely stemming from collisions at the magnetic equator. A tentative period of P approximate to 5 yr is derived from variability of the Ha line. Our study confirms that strongly magnetized stars lose little or no mass, and supplies important constraints on the weak-wind problem of massive main sequence stars. KW - stars: massive KW - stars: magnetic field KW - stars: mass-loss Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201731291 SN - 1335-1842 SN - 1336-0337 VL - 48 IS - 1 SP - 139 EP - 143 PB - Astronomický Ústav SAV CY - Tatranská Lomnica ER - TY - JOUR A1 - Bozzo, Enrico A1 - Oskinova, Lida A1 - Feldmeier, Achim A1 - Falanga, M. T1 - Clumpy wind accretion in supergiant neutron star high mass X-ray binaries JF - BMC neuroscience N2 - The accretion of the stellar wind material by a compact object represents the main mechanism powering the X-ray emission in classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. In this work we present the first attempt to simulate the accretion process of a fast and dense massive star wind onto a neutron star, taking into account the effects of the centrifugal and magnetic inhibition of accretion ("gating") due to the spin and magnetic field of the compact object. We made use of a radiative hydrodynamical code to model the nonstationary radiatively driven wind of an O-B supergiant star and then place a neutron star characterized by a fixed magnetic field and spin period at a certain distance from the massive companion. Our calculations follow, as a function of time (on a total timescale of several hours), the transitions of the system through all different accretion regimes that are triggered by the intrinsic variations in the density and velocity of the nonstationary wind. The X-ray luminosity released by the system is computed at each time step by taking into account the relevant physical processes occurring in the different accretion regimes. Synthetic lightcurves are derived and qualitatively compared with those observed from classical supergiant high mass X-ray binaries and supergiant fast X-ray transients. Although a number of simplifications are assumed in these calculations, we show that taking into account the effects of the centrifugal and magnetic inhibition of accretion significantly reduces the average X-ray luminosity expected for any neutron star wind-fed binary. The present model calculations suggest that long spin periods and stronger magnetic fields are favored in order to reproduce the peculiar behavior of supergiant fast X-ray transients in the X-ray domain. KW - stars: neutron KW - X-rays: binaries KW - supergiants Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201628341 SN - 1432-0746 VL - 589 SP - 369 EP - 389 PB - EDP Sciences CY - Les Ulis ER - TY - GEN A1 - Kubatova, B. A1 - Kubát, Jiří A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida T1 - Clumping in Massive Star Winds and its Possible Connection to the B[e] Phenomenon T2 - The B(e) Phenomenon: Forty Years of Studies : proceedings of a conference held at Charles University, Prague, Czech Republic, 27 June-1 July 2016 N2 - It has been observationally established that winds of hot massive stars have highly variable characteristics. The variability evident in the winds is believed to be caused by structures on a broad range of spatial scales. Small-scale structures (clumping) in stellar winds of hot stars are possible consequence of an instability appearing in their radiation hydrodynamics. To understand how clumping may influence calculation of theoretical spectra, different clumping properties and their 3D nature have to be taken into account. Properties of clumping have been examined using our 3D radiative transfer calculations. Effects of clumping for the case of the B[e] phenomenon are discussed. Y1 - 2017 SN - 978-1-58381-900-5 SN - 978-1-58381-901-2 VL - 508 SP - 45 EP - 50 PB - Astronomical Soceity of the Pacific CY - San Fransisco ER - TY - JOUR A1 - Oskinova, Lida A1 - Feldmeier, Achim A1 - Kretschmar, Peter T1 - Clumped stellar winds in supergiant high-mass X-ray binaries: X-ray variability and photoionization JF - Monthly notices of the Royal Astronomical Society N2 - The clumping of massive star winds is an established paradigm, which is confirmed by multiple lines of evidence and is supported by stellar wind theory. The purpose of this paper is to bridge the gap between detailed models of inhomogeneous stellar winds in single stars and the phenomenological description of donor winds in supergiant high-mass X-ray binaries (HMXBs). We use the results from time-dependent hydrodynamical models of the instability in the line-driven wind of a massive supergiant star to derive the time-dependent accretion rate on to a compact object in the BondiHoyleLyttleton approximation. The strong density and velocity fluctuations in the wind result in strong variability of the synthetic X-ray light curves. The model predicts a large-scale X-ray variability, up to eight orders of magnitude, on relatively short time-scales. The apparent lack of evidence for such strong variability in the observed HMXBs indicates that the details of the accretion process act to reduce the variability resulting from the stellar wind velocity and density jumps. KW - accretion, accretion discs KW - instabilities KW - stars: neutron KW - X-rays: binaries KW - X-rays: stars Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2966.2012.20507.x SN - 0035-8711 VL - 421 IS - 4 SP - 2820 EP - 2831 PB - Wiley-Blackwell CY - Malden ER -