Gemini/Phoenix H-band analysis of the globular cluster AL3

TL;DR

This study analyzes the chemical abundances of carbon, nitrogen, and oxygen in stars of the globular cluster AL3 using H-band spectroscopy, providing insights into its composition and radial velocity.

Contribution

It introduces a new spectral analysis code and applies it to derive elemental abundances and radial velocity for AL3 and other clusters.

Findings

C, N, and O abundances tentatively derived for AL3 stars

Cluster's radial velocity determined from spectra

Line identification in the 15555 A spectral region

Abstract

The globular cluster AL~3 is old and located in the inner bulge. Three individual stars were observed with the Phoenix spectrograph at the Gemini South telescope. The wavelength region contains prominent lines of CN, OH, and CO, allowing the derivation of C, N, and O abundances of cool stars. We aim to derive C, N, O abundances of three stars in the bulge globular cluster AL3, and additionally in stars of NGC 6558 and HP1. The spectra of AL3 allows us to derive the cluster's radial velocity. For AL3, we applied a new code to analyse its colour-magnitude diagram. Synthetic spectra were computed and compared to observed spectra for the three clusters. We present a detailed identification of lines in the spectral region centred at 15555 A, covering the wavelength range 15525-15590 A. C, N, and O abundances are tentatively derived for the sample stars.