An enquiry on the origins of N-rich stars in the inner Galaxy basedon APOGEE chemical compositions

TL;DR

This study investigates the origins of nitrogen-rich stars in the inner Galaxy, suggesting a significant fraction may be accreted from dissolved globular clusters, challenging existing models and providing new insights into Galactic evolution.

Contribution

It provides the first chemical and kinematic analysis indicating that about 30% of N-rich stars in the inner Galaxy are likely accreted, offering new constraints for globular cluster evolution models.

Findings

Approximately 30% of N-rich stars are of accreted origin.

Accreted N-rich stars have a higher specific frequency than in situ stars.

Results challenge current numerical simulations of globular cluster disruption.

Abstract

Recent evidence based on APOGEE data for stars within a few kpc of the Galactic centre suggests that dissolved globular clusters (GCs) contribute significantly to the stellar mass budget of the inner halo. In this paper we enquire into the origins of tracers of GC dissolution, N-rich stars, that are located in the inner 4 kpc of the Milky Way. From an analysis of the chemical compositions of these stars we establish that about 30% of the N-rich stars previously identified in the inner Galaxy may have an accreted origin. This result is confirmed by an analysis of the kinematic properties of our sample. The specific frequency of N-rich stars is quite large in the accreted population, exceeding that of its in situ counterparts by near an order of magnitude, in disagreement with predictions from numerical simulations. We hope that our numbers provide a useful test to models of GC formation and destruction.