Linking globular cluster structural parameters and their evolution: multiple stellar populations. (arXiv:2011.12292v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Mastrobuono_Battisti_A/0/1/0/all/0/1">Alessandra Mastrobuono-Battisti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Perets_H/0/1/0/all/0/1">Hagai B. Perets</a>
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.
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.
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