Independent Signs of Lower Mass-Loss Rates for O-Type Stars

TL;DR

Multiple lines of observational evidence suggest that the mass-loss rates of O-type stars are significantly lower than previously thought, likely due to wind clumping, which impacts stellar evolution models.

Contribution

This paper compiles independent observational constraints indicating that O-star mass-loss rates should be revised downward by a factor of three or more.

Findings

Mass-loss rates in LBV eruptions are large.

Evolved massive stars have large masses inconsistent with high steady winds.

Lower metallicity environments show reduced mass-loss signatures.

Abstract

I discuss observational evidence -- independent of the direct spectral diagnostics of stellar winds themselves -- suggesting that mass-loss rates for O stars need to be revised downward by roughly a factor of three or more, in line with recent observed mass-loss rates for clumped winds. These independent constraints include the large observed mass-loss rates in LBV eruptions, the large masses of evolved massive stars like LBVs and WNH stars, WR stars in lower metallicity environments, observed rotation rates of massive stars at different metallicity, supernovae that seem to defy expectations of high mass-loss rates in stellar evolution, and other clues. I pay particular attention to the role of feedback that would result from higher mass-loss rates, driving the star to the Eddington limit too particular attention to the role of feedback that would result from higher mass-loss rates, driving the star to the Eddington limit too soon, and therefore making higher rates appear highly implausible. Some of these arguments by themselves may have more than one interpretation, but together they paint a consistent picture that steady line-driven winds of O-type stars have lower mass-loss rates and are significantly clumped.