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 -