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 [α/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 [α/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 [α/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. ★Based on observations collected at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.