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 - 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 - 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 - 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 -