Multi-iron subpopulations in Liller 1 from high-resolution H-band spectroscopy

Abstract

We present a high-resolution chemical study of a representative sample of 21 luminous giant stars in Liller 1, a complex stellar system in the Galactic bulge, based on H-band spectra acquired with the Near-Infrared Spectrograph at KeckII. In this sample, we found fifteen stars with a subsolar iron abundance and enhanced alpha /Fe and Al/Fe likely older, having formed early and quickly from gas mainly enriched by type II supernovae, and six stars with supersolar iron and roughly solar-scaled alpha /Fe and Al/Fe likely younger, having formed at later epochs from gas also enriched by type Ia supernovae. Moreover, both subpopulations show enhanced N/Fe as in the bulge field, approximately solar-scaled V/Fe and depletion of C/Fe and 12C/13C with respect to the solar values, indicating the occurrence of significant mixing in the stellar interiors of these evolved stars. Our study also reveals that the subsolar subpopulation shows some structuring, and the presence of a third subcomponent with iron content and intermediate alpha /Fe enhancement, in between that of the metal-poor and metal-rich main subpopulations, has been statistically assessed, providing the chemical signature of both an extended star formation with multiple bursts and some self-enrichment.