The Time-Averaged Mass-Loss Rates of Red Supergiants As Revealed by their Luminosity Functions in M31 and M33 by Philip Massey et al. on Wednesday 30 November

Mass-loss in red supergiants (RSGs) is generally recognized to be episodic,

but mass-loss prescriptions fail to reflect this. Evolutionary models show that

the total amount of mass lost during this phase determines if these stars

evolve to warmer temperatures before undergoing core collapse. The current

Geneva evolutionary models mimic episodic mass loss by enhancing the quiescent

prescription rates whenever the star's outer layers exceed the Eddington

luminosity by a large factor. This results in a 20 solar-mass model undergoing

significantly more mass loss during the RSG phase than it would have otherwise,

but has little effect on models of lower masses. We can test the validity of

this approach observationally by measuring the proportion of high-luminosity

RSGs to that predicted by the models. To do this, we use our recent

luminosity-limited census of RSGs in M31 and M33, making modest improvements to

membership, and adopting extinctions based on the recent panchromatic M31 and

M33 Hubble surveys. We then compare the proportions of the highest luminosity

RSGs found to that predicted by published Geneva models, as well as to a

special set of models computed without the enhanced rates. We find good

agreement with the models which include the supra-Eddington enhanced mass loss.

The models with lower mass-loss rates predict a larger fraction of

high-luminosity RSGs than observed, and thus can be ruled out. We also use

these improved data to confirm that the upper luminosity limit of RSGs is log

L/Lo~5.4, regardless of metallicity, using our improved data on M31 and M33

plus previous results on the Magellanic Clouds.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.14147v2