Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...455..269l&link_type=abstract
Astrophysical Journal v.455, p.269
Astronomy and Astrophysics
Astronomy
218
Stars: Early-Type, Stars: Mass Loss, Stars: Supergiants, Ultraviolet: Stars
Scientific paper
The terminal velocity, υ∞, of the stellar winds of 117 stars of spectral types 0 through F has been measured from the spectra in the new Atlas of Ultraviolet P Cygni Profiles by Snow et al. For the 68 stars with the most accurate determination of υ∞ we studied the relation between υ∞ and the photospheric escape velocity, V/esc.
The ratio υ/∞/ decreases from 2.58±0.20 in O-stars to 0.72±0.15 in A and F stars. There is a clear discontinuity in this ratio near Teff ≃ 21,000 K at spectral type B1, where the ratio drops by almost a factor 2 from υ∞/υesc ≃ 2.6 at the high-temperature side υ∞/υesc ≃ 1.3 at the low-temperature side, and possibly a smaller discontinuity near Teff ≃ 10,000 K. The discontinuity near 21,000 K is due to the change in the nature of the lines that produce the radiation pressure. At Teff ≃ 21,000 K the radiation pressure is due to high- ionization lines which are largely optically thick, whereas at Teff ≃ 21,000 K the radiation pressure is due to very large numbers of low-ionization lines, which are more optically thin, Near Teff ≃ 21,000 K the winds can exist in two states: winds with high mass-loss rates and low velocities, and winds with low mass-loss rates and high velocities. This is the bistability of stellar winds for stars with Teff ≃ 21,000 K.
We present evidence that the bistability may produce a jump in the mass-loss rates of the stars near Teff ≃ 21,000 K with the higher mass-loss rates at the low temperature side of the jump. We briefly discuss the possible role of bistability in the formation of disks around B[e]-supergiants.
The observed values of υ/∞ are used to derive empirical values of the force multiplier parameter αemp that can be used to predict the terminal velocity of any early-type star with an accuracy of better than 5% with the method described in Appendix B, if the stellar parameters are known.
Lamers Henny J. G. L. M.
Lindholm Douglas M.
Snow Theodore P.
No associations
LandOfFree
Terminal Velocities and the Bistability of Stellar Winds 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 Terminal Velocities and the Bistability of Stellar Winds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Terminal Velocities and the Bistability of Stellar Winds will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1258177