http://arxiv.org/abs/2011.12292
Globular clusters (GCs) are known to host multiple stellar populations showing chemical anomalies in the content of elements lighter than Si. The origin of such anomalies and of the internal metallicity spreads observed in Galactic globular clusters is still debated. Here we analyze data compiled from the Hubble Space Telescope, ground-based surveys and Gaia DR2 and explore relationships between the structural properties of GCs and the fraction of second population (2P) stars. Given the correlations we find, we conclude that the main factors driving the formation/evolution of 2P stars are the mass, rotational velocity, the age and concentration parameter of the cluster. Furthermore, we observe that increasing cluster escape velocity corresponds to higher 2P fractions. These correlations could be consistent with an initial formation of more centrally concentrated 2P stars in deeper cluster potentials, followed by a long-term tidal stripping of stars from clusters outskirts. The latter are dominated by the more extended distributed first population (1P) stars, and therefore stronger tidal stripping would preferentially deplete the 1P population, raising the 2P fraction in the cluster. This also suggests a tighter distribution of initial 2P fractions than observed today. In addition, higher escape velocities allow better retention of low-velocity material ejected from 1P stars, providing an alternative/additional origin for the observed differences and the distributions of 2P fractions amongst GCs.
A. Mastrobuono-Battisti and H. Perets
Thu, 26 Nov 20
47/65
Comments: 16 pages, 11 figures (5 in the main text, 6 in the appendix), 7 tables (3 in the main text, 4 in the appendix). Submitted to MNRAS. Comments are welcome