A spectroscopic study of the Globular Cluster NGC 4147

TL;DR

This study provides the first detailed spectroscopic analysis of NGC 4147, revealing its chemical composition, element abundance variations, and implications for its origin and evolutionary history within the Milky Way.

Contribution

It offers the first extensive spectroscopic data on NGC 4147, detailing its chemical abundances and evidence of multiple stellar populations, and discusses its likely Galactic origin.

Findings

Metallicity of [Fe/H]=-1.84+-0.02

Presence of Na-O anti-correlation and Na-Al correlation

Only 15% of stars are first-generation, indicating significant mass loss

Abstract

We present the abundance analysis for a sample of 18 red giant branch stars in the metal-poor globular cluster NGC 4147 based on medium and high resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Y, Ba, and Eu. We find a metallicity of [Fe/H]=-1.84+-0.02 and an alpha-enhancement of +0.38+-0.05 (errors on the mean), typical of halo globular clusters in this metallicity regime. A significant spread is observed in the abundances of light elements C, N, O, Na, and Al. In particular we found a Na-O anti-correlation and Na-Al correlation. The cluster contains only 15% of stars that belong to the first generation (Na-poor and O-rich). This implies that it suffered a severe mass loss during its lifetime. Its [Ca/Fe] and [Ti/Fe] mean values agree better with the Galactic Halo trend than with the trend of extragalactic environments at the cluster metallicity. This possibly suggests that NGC 4147 is a genuine Galactic object at odd with what claimed by some author that proposed the cluster to be member of the Sagittarius dwarf galaxy. A anti-relation between the light s-process element Y and Na may also be present.