Mass loss from extreme helium stars.

Abstract

Indications of mass loss are found in the UV spectra of three extreme helium stars (HD 160641, BD -9 deg 4395, and BD +10 deg 2179) obtained with the IUE in high resolution. These three stars are found to lose mass with rates of roughly 10 to the -9th solar mass/yr. These rates have approximately the same order-of-magnitude as expected for 'normal' stars with similar luminosities (about 10,000 solar luminosities), though the final velocities of the winds are distinctly smaller in the case of these three extreme helium stars. Hence, it is stated as a general result that, in first-order approximation, mass loss rates are independent of the internal structure, evolutionary history, and chemical composition of the star. In addition, within the present sample, the mass loss rates show a decrease with increasing radius, whereas the mass and luminosity of the three program stars are similar. This behavior contradicts all theoretical predictions as well as empirical correlations obtained for early-type stars of normal composition.