Rotational Effects on the Dynamical Instability of Luminous Blue Variables

Abstract

Rotation influences the dynamical stability of a star in both direct and indirect ways. Directly, it supplies rotational kinetic energy to the star and changes the star's hydrostatic structure. Indirectly, it influences the possible course of stellar evolution. Calculations show that, for a luminous blue variable (LBV), rotation is not expected to greatly affect the onset of dynamical instability in any direct way, but could be important through its indirect evolutionary effect on the star's luminosity-to-mass ratio. If the classical LBV's are evolving in an advanced stage of central helium burning, when their envelopes are most prone to dynamical instability, the luminosity-to-mass ratio would probably be increased by rotation. It is shown that a brightening of the star lessens its dynamical stability and so leads to a somewhat hotter effective temperature during the phase of dynamical instability. How rotation modifies the Eddington luminosity limit is also discussed.