Mass fluxes for hot stars

TL;DR

This paper derives theoretical mass fluxes for hot stars to understand their low mass-loss rates, identifying a weak-wind domain and comparing predictions with observations, highlighting discrepancies and the impact of wind clumping.

Contribution

It introduces a first-principles method for calculating mass fluxes in hot stars and delineates the weak-wind domain, improving understanding of low mass-loss rates.

Findings

Weak-wind domain identified where mass loss is less than nuclear burning.

Theoretical fluxes are lower than previous empirical formulas but still do not match observations.

Predictions align with observed reductions when wind clumping is considered.

Abstract

In an attempt to understand the extraordinarily small mass-loss rates of late-type O dwarfs, mass fluxes in the relevant part of (T_{eff}, g)-space are derived from first principles using a previously-described code for constructing moving reversing layers. From these mass fluxes, a weak-wind domain is identified within which a star's rate of mass loss by a radiatively-driven wind is less than that due to nuclear burning. The five weak-wind stars recently analysed by Marcolino et al. (2009) fall within or at the edge of this domain. But although the theoretical mass fluxes for these stars are ~ 1.4 dex lower than those derived with the formula of Vink et al. (2000), the observed rates are still not matched, a failure that may reflect our poor understanding of low-density supersonic outflows. Mass fluxes are also computed for two strong-wind O4 stars analysed by Bouret et al. (2005). The predictions agree with the sharply reduced mass loss rates found when Bouret et al. take wind clumping into account.