Mass Loss by Hot Stars

A mechanism is proposed to explain the mass loss observed for luminous, hot stars. We show that the ultraviolet resonance lines of ions such as Si iv, C iv, N v, and S vi can give strongly negative effective gravities in the outer parts of the reversing layers of hot stars. We argue that a static reversing layer is then no longer possible and that a continuous outflow of mass occurs. To calculate rates of mass loss resulting from this mechanism, we formulate the problem of steady-state, moving reversing layers. From numerical solutions of the equations of this problem, the rate of mass loss is found to be < L/c2 the evolution of the star is therefore not disturbed significantly. The domain in the (log , log g)-plane where the greatest rates of mass loss are expected is also approximately determined and found to be roughly consistent with observation. Finally, the problem of the supersonic flow to large distances from the star is briefly discussed.