Is mass loss along the red giant branch of globular clusters sharply peaked? The case of M3

TL;DR

This paper models the horizontal branch and RR Lyrae period distribution in globular cluster M3, showing that a very small dispersion in mass loss and helium variation explain observed features, challenging previous assumptions.

Contribution

It demonstrates that a minimal mass loss dispersion and helium variation can accurately reproduce M3's horizontal branch and RR Lyrae period distribution, offering new insights into stellar evolution.

Findings

Mass loss dispersion must be less than ~0.003 Msun.

Helium content variation explains horizontal branch extension.

Small mass loss variation reproduces RR Lyrae period distribution.

Abstract

There is a growing evidence that several globular clusters must contain multiple stellar generations, differing in helium content. This hypothesis has helped to interpret peculiar unexplained features in their horizontal branches. In this framework we model the peaked distribution of the RR Lyr periods in M3, that has defied explanation until now. At the same time, we try to reproduce the colour distribution of M3 horizontal branch stars. We find that only a very small dispersion in mass loss along the red giant branch reproduces with good accuracy the observational data. The enhanced and variable helium content among cluster stars is at the origin of the extension in colour of the horizontal branch, while the sharply peaked mass loss is necessary to reproduce the sharply peaked period distribution of RR Lyr variables. The dispersion in mass loss has to be <~ 0.003 Msun, to be compared with the usually assumed values of ~0.02 Msun. This requirement represents a substantial change in the interpretation of the physical mechanisms regulating the evolution of globular cluster stars.