Analysis of integrated-light spectra of Galactic globular clusters

TL;DR

This study analyzes integrated-light spectra of 26 Galactic globular clusters to determine their ages, chemical compositions, and helium content, validating the method against existing literature and exploring stellar evolution effects.

Contribution

The paper introduces an improved method for analyzing integrated-light spectra, including automatic microturbulence calculation, to accurately determine chemical abundances and ages of globular clusters.

Findings

Chemical abundances mostly agree with literature values.

Estimated ages and helium fractions align with previous CMD analyses.

Systematic differences in carbon suggest atmospheric changes during stellar evolution.

Abstract

We present the results of determination of the age, helium mass fraction (Y) in terms of the used stellar evolutionary models, metallicity ([Fe/H]), and abundances of the elements C, O, Na, Mg, Ca, Ti, Cr and Mn for 26 globular clusters of the Galaxy. In this work, we apply a method developed by us that employs medium-resolution integrated-light spectra of globular clusters and models of stellar atmospheres and it is supplemented in this paper by the automatic calculation of microturbulence velocities of stars in the studied objects. Based on the data obtained for 26 objects, as well as on the results of our previous studies, it is shown that the abundances of chemical elements, that we measured, with the exception of carbon, are consistent with the literature estimates from the analysis of integrated-light spectra of clusters and from high-resolution spectroscopic observations of their brightest stars. Our estimates of [C/Fe] are consistent with the literature values obtained from the integrated-light spectra of clusters. We interpret the systematic difference between the derived [C/Fe] for globular clusters and the literature [C/Fe] values for the brightest stars of the clusters as a change of the chemical composition in the atmospheres of stars during their evolution. The estimated absolute ages and average Y for the clusters are in a reasonable agreement with the literature data from the analysis of color magnitude diagrams of the objects.