The parent populations of six groups identified from chemical tagging in the solar neighbourhood

We estimate the size and distribution of the parent populations for the six largest (at least 20 stars in the solar neighbourhood) chemical groups identified in the chemical tagging experiment by Mitschang et al. 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 neighbourhood and where orbits have apocentre 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 disc groups have narrowangular 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 disc groups exhibit both wide angular momentum and eccentricity distributions implying that both heating and radial migration has taken place.