Mass loss of hot luminous stars
Abstract
The concept of radiation driven winds is reviewed with respect to the observed properties of mass-loss in massive OB-stars. It is shown that the recent improvements of radiation driven wind theory lead to a much better agreement with the observations and allow to reproduce the observed values of mass-loss rate and terminal velocities. This includes not only galactic O-stars and extreme B-supergiants like P Cygni but also the massive stars in galaxies of lower metallicity like the O-stars in the Magellanic Clouds. It is also shown that detailed non-LTE multi level calculations including electron collisions are necessary to describe the ionization and excitation of stellar winds properly. The full treatment of the statistical equilibrium for all relevant ions from H to Zn simultaneously together with the radiation hydrodynamics of cool O-star winds leads to a significant shift to higher ionization stages. This is caused by collisional excitation of low lying excited levels and subsequent photoionization from these levels. As a result high ionization species like O VI, S VI, N V etc. can be easily produced in a cool wind model for ζ Puppis. Thus the longstanding problem of superionization can be solved without any other source of ionization.
- Publication:
-
New Insights in Astrophysics. Eight Years of UV Astronomy with IUE
- Pub Date:
- September 1986
- Bibcode:
- 1986ESASP.263..247K
- Keywords:
-
- Astrophysics;
- B Stars;
- O Stars;
- Stellar Mass Ejection;
- Stellar Radiation;
- Stellar Winds;
- Photoionization;
- Stellar Models;
- Terminal Velocity;
- Ultraviolet Astronomy