Detailed Abundances of 15 Stars in the Metal-Poor Globular Cluster NGC 4833

TL;DR

This study provides detailed chemical abundance measurements for 15 stars in the metal-poor globular cluster NGC 4833, confirming uniform metallicity and typical r-process enrichment, with no evidence of actinide boost.

Contribution

First detailed abundance analysis of 15 stars in NGC 4833, including 43 species, confirming no internal metallicity spread and typical r-process enrichment patterns.

Findings

No internal metallicity spread in NGC 4833

Abundance variations among light elements like C, N, O, Na, Mg, Al

Heavy-element distribution shows r-process enrichment, no actinide boost

Abstract

We have observed 15 red giant stars in the relatively massive, metal-poor globular cluster NGC 4833 using the Magellan Inamori Kyocera Echelle spectrograph at Magellan. We calculate stellar parameters for each star and perform a standard abundance analysis to derive abundances of 43 species of 39 elements, including 20 elements heavier than the iron group. We derive <[Fe/H]> = -2.25 +/- 0.02 from Fe I lines and <[Fe/H> = -2.19 +/- 0.013 from Fe II lines. We confirm earlier results that found no internal metallicity spread in NGC 4833, and there are no significant star-to-star abundance dispersions among any elements in the iron group (19 <= Z <= 30). We recover the usual abundance variations among the light elements C, N, O, Na, Mg, Al, and possibly Si. The heavy-element distribution reflects enrichment by r-process nucleosynthesis ([Eu/Fe] = +0.36 +/- 0.03), as found in many other metal-poor globular clusters. We investigate small star-to-star variations found among the neutron-capture elements, and we conclude that these are probably not real variations. Upper limits on the Th abundance, log epsilon (Th/Eu) < -0.47 +/- 0.09, indicate that NGC 4833, like other globular clusters where Th has been studied, did not experience a so-called "actinide boost."