Study of Integrated Spectra of Four Globular Clusters in M31

TL;DR

This study analyzes the chemical composition, age, and metallicity of four globular clusters in M31 using moderate resolution spectra, providing new data on their properties and comparing them to the galaxy's halo stars.

Contribution

First determination of chemical composition and helium fraction for two clusters, and comprehensive spectral analysis of four clusters in M31.

Findings

All clusters are older than 11 Gyr.

Metallicities range from -1.1 to -0.75 dex.

Element abundances match the inner halo of M31.

Abstract

The results of determining the metallicity, age, helium mass fraction (Y) and abundances of the elements C, N, Mg, Ca, Mn, Ti and Cr by moderate resolution spectra for four globular clusters in the galaxy M 31: Bol 6, Bol 20, Bol 45 and Bol 50 are presented. The chemical composition for Bol 20 and Bol 50, and Y for four clusters are determined for the first time. The spectra of the studied objects were obtained with the 6-meter telescope of the SAO RAS in 2020. All the clusters under study turned out to be older than 11 Gyrs. The determined metallicities [Fe/H] are in the range from -1.1 to -0.75 dex. They are lower than the metallicity of stars of the M 31 halo at a given distance from the galactic center (R_M31 < 10 kpc). The abundances of the elements of the alpha-process [alpha/Fe] = ([O/Fe] + [Mg/Fe] + [Ca/Fe])/3 of the four clusters correspond to those of the stars of the inner halo of M31.