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

TL;DR

This study reveals multiple iron subpopulations in Liller 1, showing different ages and chemical enrichment histories, indicating complex formation and star formation processes in this Galactic bulge system.

Contribution

First high-resolution H-band spectroscopic analysis of Liller 1 revealing multiple iron subpopulations and their chemical properties.

Findings

Identification of two main subpopulations with distinct iron abundances.

Evidence of a third intermediate subcomponent with mixed properties.

Indication of extended star formation with multiple bursts and self-enrichment.

Abstract

We present a high resolution chemical study of a representative sample of 21 luminous giant stars of Liller~1, a complex stellar system in the Galactic bulge, based on H band spectra acquired with the Near InfraRed Spectrograph at KeckII. 15 stars turn out to have a subsolar iron abundance and enhanced [$\alpha$/Fe] and [Al/Fe], likely old that formed early and quickly from gas mainly enriched by type~II supernovae, and 6 stars with supersolar iron and roughly solar-scaled [$\alpha$/Fe] and [Al/Fe], likely younger, thus formed at later epochs from gas also enriched by type~Ia supernovae. Moreover, both subpopulations show enhanced [N/Fe], as in the bulge field, about solar-scaled [V/Fe], and depletion of [C/Fe] and $^{12}$C/$^{13}$C with respect to the solar values, indicating the occurrence of significant mixing in the stellar interiors of these evolved stars. The current study has also made evident that the sub-solar subpopulation shows some structuring, and the presence of a third subcomponent with iron content and [$\alpha$/Fe] enhancement somewhat intermediate between the metal-poor and metal-rich main subpopulations, has been statistically assessed, providing the chemical signature of an extended star formation with multiple bursts and of some self-enrichment.