Mass-loss law for red giant stars in simple population globular clusters

Abstract

The amount of mass lost by stars during the red-giant branch (RGB) phase is one of the main parameters to understand and correctly model the late stages of stellar evolution. Nevertheless, a fully-comprehensive knowledge of the RGB mass loss is still missing. Galactic Globular Clusters (GCs) are ideal targets to derive empirical formulations of mass loss, but the presence of multiple populations with different chemical compositions has been a major challenge to constrain stellar masses and RGB mass losses. Recent work has disentangled the distinct stellar populations along the RGB and the horizontal branch (HB) of 46 GCs, thus providing the possibility to estimate the RGB mass loss of each stellar population. The mass losses inferred for the stellar populations with pristine chemical composition (called first-generation or 1G stars) tightly correlate with cluster metallicity. This finding allows us to derive an empirical RGB mass-loss law for 1G stars. In this paper we investigate seven GCs with no evidence of multiple populations and derive the RGB mass loss by means of high-precision Hubble-Space Telescope photometry and accurate synthetic photometry. We find a cluster-to-cluster variation in the mass loss ranging from ∼0.1 to ∼0.3 M⊙. The RGB mass loss of simple-population GCs correlates with the metallicity of the host cluster. The discovery that simple-population GCs and 1G stars of multiple population GCs follow similar mass-loss vs. metallicity relations suggests that the resulting mass-loss law is a standard outcome of stellar evolution.

Constraining the original composition of the gas forming first-generation stars in globular clusters

“…In this context, the evidence that 1G stars of M 3-and M 13like GCs exhibit different internal iron variations may indicate different properties of the formation environment. Specifically, the smaller iron variation of M 13-like GCs is consistent with a scenario where these clusters formed in high-density environments as suggested by Tailo et al (2019aTailo et al ( ,b, 2020Tailo et al ( , 2021 based on the larger amount of RGB mass loss of 1G stars in these clusters.…”

“…Another distinctive feature of M 13-like clusters is that their 1G stars suffer higher RGB mass loss than 1G stars of M 3-like GCs and stars in simplepopulation GCs(Tailo et al 2020(Tailo et al , 2021. For this reason, the authors suggested that 1G stars of M 13-like GCs form in high-density environments.…”

Multiple Populations in Star Clusters

“…Remarkable examples of simple population Galactic GCs comprise Ruprecht 106 and Terzan 7, which according to both spectroscopic studies and multiband photometry are consistent with simple populations [162][163][164]. Additional candidate simple population GCs comprise AM1, Eridanus, Palomar 3, Palomar 4, Palomar 14, and Pyxis, as inferred from their HB morphology [76,165]. • GC specificity.…”

Asteroseismology of the multiple stellar populations in the Globular Cluster M4

“…This divergent behaviour could be connected to different environmental factors (interaction with the Galaxy or different formation environment), be the footprint of early dynamical interaction between the stars in GCs (stellar collisions and binaries), be the product of some still poorly understood physics inside RGB stars (like the mechanism proposed in Fusi-Pecci & Renzini 1975, 1976, or even a combination of all the previous. Indeed, the extensive study performed in Tailo et al (2020Tailo et al ( ,2021 shows that the large population of GCs analysed lies on a relation systematically higher than the one for the open clusters and the field stars of comparable metallicity (where the comparison is possible). Furthermore, said relation is compatible with the ones obtained for dwarf spheroidal galaxies (e.g.…”