TY  - JOUR
A1  - Grinberg, Victoria
A1  - Hell, Natalie
A1  - El Mellah, Ileyk
A1  - Neilsen, Joseph
A1  - Sander, Andreas Alexander Christoph
A1  - Leutenegger, Maurice
A1  - Fürst, Felix
A1  - Huenemoerder, David P.
A1  - Kretschmar, Peter
A1  - Kuehnel, Matthias
A1  - Martinez-Nunez, Silvia
A1  - Niu, Shu
A1  - Pottschmidt, Katja
A1  - Schulz, Norbert S.
A1  - Wilms, Joern
A1  - Nowak, Michael A.
T1  - The clumpy absorber in the high-mass X-ray binary Vela X-1
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Bright and eclipsing, the high-mass X-ray binary Vela X-1 offers a unique opportunity to study accretion onto a neutron star from clumpy winds of O/B stars and to disentangle the complex accretion geometry of these systems. In Chandra-HETGS spectroscopy at orbital phase similar to 0.25, when our line of sight towards the source does not pass through the large-scale accretion structure such as the accretion wake, we observe changes in overall spectral shape on timescales of a few kiloseconds. This spectral variability is, at least in part, caused by changes in overall absorption and we show that such strongly variable absorption cannot be caused by unperturbed clumpy winds of O/B stars. We detect line features from high and low ionization species of silicon, magnesium, and neon whose strengths and presence depend on the overall level of absorption. These features imply a co-existence of cool and hot gas phases in the system, which we interpret as a highly variable, structured accretion flow close to the compact object such as has been recently seen in simulations of wind accretion in high-mass X-ray binaries.
KW  - X-rays: individuals: Vela X-1
KW  - X-rays: binaries
KW  - stars: winds, outflows
KW  - stars: massive
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201731843
SN  - 1432-0746
VL  - 608
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Martinez-Nunez, Silvia
A1  - Sander, Angelika
A1  - Gimenez-Garcia, Angel
A1  - Gonzalez-Galan, Ana
A1  - Torrejon, Jose Miguel
A1  - Gonzalez-Fernandez, Carlos
A1  - Hamann, Wolf-Rainer
T1  - The donor star of the X-ray pulsar X1908+075
JF  - Astronomy and astrophysics : an international weekly journal
N2  - High-mass X-ray binaries consist of a massive donor star and a compact object. While several of those systems have been well studied in X-rays, little is known for most of the donor stars as they are often heavily obscured in the optical and ultraviolet regime. There is an opportunity to observe them at infrared wavelengths, however. The goal of this study is to obtain the stellar and wind parameters of the donor star in the X1908+075 high-mass X-ray binary system with a stellar atmosphere model to check whether previous studies from X-ray observations and spectral morphology lead to a sufficient description of the donor star. We obtained H-and K-band spectra of X1908+075 and analysed them with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. For the first time, we calculated a stellar atmosphere model for the donor star, whose main parameters are: M-spec = 15 +/- 6 M-circle dot, T-* = 23(-3)(+6) kK, log g(eff) = 3.0 +/- 0.2 and log L/L-circle dot = 4.81 +/- 0.25. The obtained parameters point towards an early B-type (B0-B3) star, probably in a supergiant phase. Moreover we determined a more accurate distance to the system of 4.85 +/- 0.50 kpc than the previously reported value.
KW  - binaries: close
KW  - stars: individual: X1908+075
KW  - stars: massive
KW  - stars: winds
KW  - outflows
KW  - X-rays: binaries
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201424823
SN  - 0004-6361
SN  - 1432-0746
VL  - 578
PB  - EDP Sciences
CY  - Les Ulis
ER  -