Theoretical evolution of massive stars with mass loss by stellar wind.

Abstract

Although it was known since a long time that very luminous blue and red stars may show evidence of mass outflow, it was the advent of the Copernicus satellite that clearly ascertained all OB supergiants (and also the most luminous main sequence stars) are losing mass at rates that are significant for their evolutionary history. The observational information for blue luminous stars (O, Of and WR) has been recently reviewed by Conti (1978), who discussed in some detail the data available for different spectral regions. The rates of mass loss inferred from these observations are estimated to be in the range 10−7to 10−5M⊙/yr for OB stars, and from 10−5to 10−4M⊙/yr for WR stars. Several theoretical models have been proposed to explain those high mass-loss rates, and the high terminal velocities ranging from 1000 to 3000 km/sec. The two basic models are: the cool radiation pressure model, originally proposed by Lucy and Solomon (1970) and elaborated by Castor et al. (1975), in which the envelope is accelerated by momentum transfer from radiation to ions due to the ultraviolet line absorption; and the coronal model of Thomas (1973), and Hearn (1975), where the wind is sustained by gas pressure in a hot corona around the star. As both models do not completely account for the observations, several complementary modifications have been suggested. The nowaday situation is reviewed by Cassinelli and Lamers (1978), and Conti (1978).