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  - 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  -