@article{MartinezNunezSanderGimenezGarciaetal.2015,
  author    = {Martinez-Nunez, Silvia and Sander, Angelika and Gimenez-Garcia, Angel and Gonzalez-Galan, Ana and Torrejon, Jose Miguel and Gonzalez-Fernandez, Carlos and Hamann, Wolf-Rainer},
  title     = {The donor star of the X-ray pulsar X1908+075},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {578},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/201424823},
  pages     = {9},
  year      = {2015},
  abstract  = {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.},
  language  = {en}
}
@article{TodtSanderHainichetal.2015,
  author    = {Todt, Helge Tobias and Sander, Angelika and Hainich, Rainer and Hamann, Wolf-Rainer and Quade, Markus and Shenar, Tomer},
  title     = {Potsdam Wolf-Rayet model atmosphere grids for WN stars},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {579},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/201526253},
  pages     = {6},
  year      = {2015},
  abstract  = {We present new grids of Potsdam Wolf-Rayet (PoWR) model atmospheres for Wolf-Rayet stars of the nitrogen sequence (WN stars). The models have been calculated with the latest version of the PoWR stellar atmosphere code for spherical stellar winds. The WN model atmospheres include the non-LTE solutions of the statistical equations for complex model atoms, as well as the radiative transfer equation in the co-moving frame. Iron-line blanketing is treated with the help of the superlevel approach, while wind inhomogeneities are taken into account via optically thin clumps. Three of our model grids are appropriate for Galactic metallicity. The hydrogen mass fraction of these grids is 50\%, 20\%, and 0\%, thus also covering the hydrogen-rich late-type WR stars that have been discovered in recent years. Three grids are adequate for LMC WN stars and have hydrogen fractions of 40\%, 20\%, and 0\%. Recently, additional grids with SMC metallicity and with 60\%, 40\%, 20\%, and 0\% hydrogen have been added. We provide contour plots of the equivalent widths of spectral lines that are usually used for classification and diagnostics.},
  language  = {en}
}