Modeling and Analysis of a Spectrum of the Globular Cluster NGC 2419

TL;DR

This study models the stellar population of the distant globular cluster NGC 2419 using integrated light spectroscopy and population synthesis, revealing its age, metallicity, and chemical peculiarities.

Contribution

It introduces a method for analyzing the integrated light spectra of globular clusters to determine their properties, including chemical abundances, without relying solely on high-resolution spectroscopy of individual stars.

Findings

Derived age of 12.6 Gyr and [Fe/H]=-2.25 dex for NGC 2419.

Identified a lower [alpha/Fe] ratio (0.13 dex) compared to previous high-resolution studies.

Confirmed chemical peculiarities and abundance dispersions in the cluster.

Abstract

NGC 2419 is the most distant massive globular cluster in the outer Galactic halo. It is unusual also due to the chemical peculiarities found in its red giant stars in recent years. We study the stellar population of this unusual object using spectra obtained at the 1.93-m telescope of the Haute-Provence Observatory. At variance with commonly used methods of high-resolution spectroscopy applicable only to bright stars, we employ spectroscopic information on the integrated light of the cluster. We carry out population synthesis modeling of medium-resolution spectra using synthetic stellar atmosphere models based on a theoretical isochrone corresponding accurately to the observed color-magnitude diagram. We study the influence of non-Local Thermodynamic Equilibrium for some chemical elements on our results. The derived age (12.6 Gyr), [Fe/H]=-2.25 dex, helium content Y=0.25, and abundances of 12 other chemical elements are in a good qualitative agreement with published high-resolution spectroscopy estimates for red giant members in the cluster. On the other hand, the derived element abundance, [alpha/Fe]=0.13 dex (the mean of [O/Fe], [Mg/Fe] and [Ca/Fe]), differs from the published one ([alpha/Fe] =0.4 dex) for selected red giants in the cluster and may be explained by a large dispersion in the alpha-element abundances recently discovered in NGC2419. We suggest that studies of the {\it integrated} light in the cluster using high-resolution spectrographs in different wavelength regions will help to understand the nature of these chemical anomalies.