The Parent Populations of 6 groups identified from Chemical Tagging in the Solar neighborhood

TL;DR

This study estimates the size and distribution of the parent stellar populations for six chemically identified groups in the Solar neighborhood, revealing insights into their origins and migration histories.

Contribution

It provides the first estimates of the parent populations' sizes and distributions for these chemical groups, linking their orbital properties to Galactic dynamics.

Findings

Parent populations contain at least 200,000 stars.

Thin disk groups show narrow angular momentum distributions with limited migration.

Thick disk groups exhibit wide distributions indicating heating and radial migration.

Abstract

We estimate the size and distribution of the parent populations for the 6 largest (at least 20 stars in the Solar neighborhood) chemical groups identified in the Chemical Tagging experiment by Mitschang et al.~2014. Stars in the abundance groups tend to lie near a boundary in angular momentum versus eccentricity space where the probability is highest for a star to be found in the Solar neighborhood and where orbits have apocenter approximately equal to the Sun's galactocentric radius. Assuming that the parent populations are uniformly distributed at all azimuthal angles in the Galaxy, we estimate that the parent populations of these abundance groups contain at least 200,000 members. The spread in angular momentum of the groups implies that the assumption of a uniform azimuthal distribution only fails for the two youngest groups and only for the highest angular momentum stars in them. The parent populations of three thin disk groups have narrow angular momentum distributions, but tails in the eccentricity and angular momentum distributions suggest that only a small fraction of stars have migrated and increased in eccentricity. In contrast, the parent populations of the thick disk groups exhibit both wide angular momentum and eccentricity distributions implying that both heating and radial migration has taken place.