Mass-loss from multiple populations: hint of a universal mass loss-law for Pop II stars?

Poster for the Cool stars 20.5 virtual conference.

Abstract:

The amount of mass lost by stars during the red-giant branch (RGB) phase is one of the main parameters to correctly study later stages of stellar evolution. In spite of its importance, a fully-comprehensive understanding of this phenomenon is still missing and we mostly rely on empirical formulations. The Galactic Globular Clusters (GCs) are ideal targets to derive such formulations of mass loss, but the presence of multiple populations has been a major challenge.
We combine Hubble Space Telescope photometry with stellar evolutionary models, to analyse the horizontal branch (HB) stars in 53 GCs. We constrained the helium abundance for the first and the “extreme” second generations stars using independent measurements based on the RGB. With these new constrains the parameters degeneracy traditionally associated to these stars has been broken for the first time.

Our main results are: the mass loss of first generation stars is tightly correlated with cluster metallicity; the location of helium enriched stars on the HB is reproduced only by adopting a higher RGB mass loss, compared to the first generation; and, finally, the difference in mass loss tightly correlates with helium enhancement and cluster mass.