Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000astl...26..660k&link_type=abstract
Astronomy Letters, Volume 26, Issue 10, October 2000, pp.660-667
Astronomy and Astrophysics
Astronomy
Scientific paper
We show that hydrostatically equilibrium models for the thin photospheres of helium stars based on new opacities k_R (OPAL and OP) can be constructed only for masses M < 5 M_solar. The parameter Gamma = kL/4GMc, defined as the ratio of light pressure to gravity, exceeds a critical value of 1.0 for larger masses, which must result in mass outflow under light pressure. This mass limit matches the observed lower limit for the masses of Wolf-Rayet stars (MWR > 5 M_solar), which is an additional argument that the Wolf-Rayet stellar cores are actually helium stars. By solving the equation of radiative transfer in extended kKatmospheres, we construct a semiempirical model for a WN5 star (MWN5 = 10 M_solar) with a helium core and an expanding envelope, whose physical and geometric parameters are known mainly from light-curve solution for the eclipsing binary V444 Cyg (WN5 + 06): outflow rate M-dot = 1.0 x 10^{-5} M_solar/yr, terminal velocity V_infty = 2000 km/s, and expanding-envelope optical depth tau_env = 25. The temperature at the outer boundary of the photosphere of a helium star surrounded by such an envelope is approximately 130 kK higher than that in the absence of an envelope, being Tph = 240 kK. Because of the high temperatures, the absorption coefficients at the corresponding photospheric levels are smaller than those in models with no envelope; therefore, the photosphere turns out to be in hydrostatic equilibrium and stable against light pressure (Gamma_max = 0.9). As a way out of this conflicting situation (an expanding envelope together with a hydrostatically equilibrium photosphere), we propose a model of discrete mass outflow, which is also supported by the observed cloudy structure of the envelopes in this type of stars. To quantitatively estimate parameters of the nonuniform outflow model requires detailed gas-dynamical calculations.
Khaliullin Kh. F.
Khaliullina A. I.
No associations
LandOfFree
Unsteady Mass Outflow from Wolf-Rayet Stars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Unsteady Mass Outflow from Wolf-Rayet Stars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Unsteady Mass Outflow from Wolf-Rayet Stars will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1769919