RADIATIVE INSTABILITY IN STELLAR ENVELOPES

摘要

A general analytic criterion for radiative instability in the envelope of a nonexplosive star is derived, based on a generalization of the Eddington limit for the star's luminosity, an expression for the stationary mass-loss acceleration, and an assumed universality of the critical mean density of the envelope. The derived criterion has been formulated as the minimum rate of mass loss needed to achieve a super-Eddington state. Expressed as a simple function of luminosity and effective temperature, it is applied to luminous blue variables (LBVs), Wolf-Rayet stars, and ordinary B-type supergiants. Assuming that the brightest LBVs as well as most of the Wolf-Rayet stars are post-main-sequence objects, these objects must have radiatively unstable envelopes.