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2011MNRAS.416.1456O - Mon. Not. R. Astron. Soc., 416, 1456-1474 (2011/September-2)
Early magnetic b-type stars: X-ray emission and wind properties.
OSKINOVA L.M., TODT H., IGNACE R., BROWN J.C., CASSINELLI J.P. and HAMANN W.-R.
Abstract (from CDS):
We analyse the ultraviolet (UV) spectra of five non-supergiant B stars with magnetic fields (τ Sco, β Cep, ξ1 CMa, V2052 Oph and ζ Cas) by means of non-local thermodynamic equilibrium (non-LTE) iron-blanketed model atmospheres. The latter are calculated with the Potsdam Wolf–Rayet (PoWR) code, which treats the photosphere as well as the wind, and also accounts for X-rays. With the exception of τ Sco, this is the first analysis of these stars by means of stellar wind models. Our models accurately fit the stellar photospheric spectra in the optical and the UV. The parameters of X-ray emission, temperature and flux are included in the model in accordance with observations. We confirm the earlier findings that the filling factors of X-ray emitting material are very high.
Our analysis reveals that the magnetic early-type B stars studied here have weak winds with velocities not significantly exceeding vesc. The mass-loss rates inferred from the analysis of UV lines are significantly lower than predicted by hydrodynamically consistent models. We find that, although the X-rays strongly affect the ionization structure of the wind, this effect is not sufficient in reducing the total radiative acceleration. When the X-rays are accounted for at the intensity and temperatures observed, there is still sufficient radiative acceleration to drive a stronger mass-loss than we empirically infer from the UV spectral lines.
Abstract Copyright: 2011 The Authors Monthly Notices of the Royal Astronomical Society2011 RAS
Journal keyword(s): techniques: spectroscopic - stars: magnetic field - stars: massive - stars: mass loss - X-rays: stars
Simbad objects: 21
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