@article{KurfuerstFeldmeierKrticka2018,
  author    = {Kurf{\"u}rst, P. and Feldmeier, Achim and Krticka, Jiri},
  title     = {Two-dimensional modeling of density and thermal structure of dense circumstellar outflowing disks},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {613},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/201731300},
  pages     = {24},
  year      = {2018},
  abstract  = {Context. Evolution of massive stars is affected by a significant loss of mass either via (nearly) spherically symmetric stellar winds or by aspherical mass-loss mechanisms, namely the outflowing equatorial disks. However, the scenario that leads to the formation of a disk or rings of gas and dust around massive stars is still under debate. It is also unclear how various forming physical mechanisms of the circumstellar environment affect its shape and density, as well as its kinematic and thermal structure. Results. Our models show the geometric distribution and contribution of viscous heating that begins to dominate in the central part of the disk for mass-loss rates higher than (M) over dot greater than or similar to 10(-10) M-circle dot yr(-1). In the models of dense viscous disks with (M) over dot > 10(-8) M-circle dot yr(-1), the viscosity increases the central temperature up to several tens of thousands of Kelvins, however the temperature rapidly drops with radius and with distance from the disk midplane. The high mass-loss rates and high viscosity lead to instabilities with significant waves or bumps in density and temperature in the very inner disk region. Conclusions. The two-dimensional radial-vertical models of dense outflowing disks including the full Navier-Stokes viscosity terms show very high temperatures that are however limited to only the central disk cores inside the optically thick area, while near the edge of the optically thick region the temperature may be low enough for the existence of neutral hydrogen, for example.},
  language  = {en}
}
@article{ReindlBainbridgePrzybillaetal.2018,
  author    = {Reindl, Nicole and Bainbridge, M. and Przybilla, Norbert and Geier, Stephan Alfred and Prvak, M. and Krticka, Jiri and Ostensen, R. H. and Telting, J. and Werner, K.},
  title     = {Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {482},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {1},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnrasl/sly191},
  pages     = {L93 -- L98},
  year      = {2018},
  abstract  = {The presence of ultrahigh excitation (UHE) absorption lines (e.g. OVIII) in the optical spectra of several of the hottest white dwarfs poses a decades-long mystery and is something that has never been observed in any other astrophysical object. The occurrence of such features requires a dense environment with temperatures near 10(6) K, by far exceeding the stellar effective temperature. Here we report the discovery of a new hot wind white dwarf, GALEXJ014636.8+323615. Astonishingly, we found for the first time rapid changes of the equivalent widths of the UHE features, which are correlated to the rotational period of the star (P=0.242035 d). We explain this with the presence of a wind-fed circumstellar magnetosphere in which magnetically confined wind shocks heat up the material to the high temperatures required for the creation of the UHE lines. The photometric and spectroscopic variability of GALEXJ014636.8+323615 can then be understood as consequence of the obliquity of the magnetic axis with respect to the rotation axis of the white dwarf. This is the first time a wind-fed circumstellar magnetosphere around an apparently isolated white dwarf has been discovered and finally offers a plausible explanation of the ultrahot wind phenomenon.},
  language  = {en}
}
@article{ToalaOskinovaHamannetal.2018,
  author    = {Toala, Jes{\´u}s Alberto and Oskinova, Lida and Hamann, Wolf-Rainer and Ignace, Richard and Sander, Andreas Alexander Christoph and Shenar, Tomer and Todt, Helge Tobias and Chu, Y. -H. and Guerrero, Martin A. and Hainich, Rainer and Torrejon, Jose Miguel},
  title     = {On the Apparent Absence of Wolf-Rayet plus Neutron Star Systems},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters},
  volume    = {869},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters},
  number    = {1},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {2041-8205},
  doi       = {10.3847/2041-8213/aaf39d},
  pages     = {5},
  year      = {2018},
  abstract  = {Among the different types of massive stars in advanced evolutionary stages is the enigmatic WN8h type. There are only a few Wolf-Rayet (WR) stars with this spectral type in our Galaxy. It has long been suggested that WN8h-type stars are the products of binary evolution that may harbor neutron stars (NS). One of the most intriguing WN8h stars is the runaway WR 124 surrounded by its magnificent nebula M1-67. We test the presence of an accreting NS companion in WR 124 using similar to 100 ks long observations by the Chandra X-ray observatory. The hard X-ray emission from WR 124 with a luminosity of L-X similar to 10(31) erg s(-1) is marginally detected. We use the non-local thermodynamic equilibrium stellar atmosphere code PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star is effectively opaque for X-rays, hence the low X-ray luminosity of WR 124 does not rule out the presence of an embedded compact object. We suggest that, in general, high-opacity WR winds could prevent X-ray detections of embedded NS, and be an explanation for the apparent lack of WR+NS systems.},
  language  = {en}
}
@article{VosVuckovicChenetal.2018,
  author    = {Vos, Joris and Vuckovic, Maja and Chen, Xuefei and Han, Zhanwen and Boudreaux, Thomas and Barlow, Brad N. and Ostensen, Roy and N{\´e}meth, P{\´e}ter},
  title     = {The orbital period-mass ratio relation of wide sdB plus MS binaries and its application to the stability of RLOF},
  series = {Monthly notices of the Royal Astronomical Society},
  volume    = {482},
  journal   = {Monthly notices of the Royal Astronomical Society},
  number    = {4},
  publisher = {Oxford Univ. Press},
  address   = {Oxford},
  issn      = {0035-8711},
  doi       = {10.1093/mnras/sty3017},
  pages     = {4592 -- 4605},
  year      = {2018},
  abstract  = {Wide binaries with hot subdwarf-B (sdB) primaries and main sequence companions are thought to form only through stable Roche-lobe overflow (RLOF) of the sdB progenitor near the tip of the red giant branch (RGB). We present the orbital parameters of 11 new long-period composite sdB binaries based on spectroscopic observations obtained with the UVES, FEROS, and CHIRON spectrographs. Using all wide sdB binaries with known orbital parameters, 23 systems, the observed period distribution is found to match very well with theoretical predictions. A second result is the strong correlation between the orbital period (P) and the mass ratio (q) in the observed wide sdB binaries. In the P-q plane two distinct groups emerge, with the main group (18 systems) showing a strong correlation of lower mass ratios at longer orbital periods. The second group comprises systems that are thought to be formed from higher mass progenitors. Based on theoretical models, a correlation between the initial mass ratio at the start of RLOF and core mass of the sdB progenitor is found, which defines a mass-ratio range at which RLOF is stable on the RGB.},
  language  = {en}
}