Discovery of relatively hydrogen-poor giants in the Galactic globular cluster Omega Centauri

TL;DR

This study identifies hydrogen-deficient red giants in Omega Centauri through spectroscopic analysis, revealing a new population of helium-enriched stars with unusually weak MgH bands.

Contribution

It reports the discovery of hydrogen-poor giants in Omega Centauri, suggesting the existence of helium-enriched stellar populations within the cluster.

Findings

Four giants with weak/absent MgH bands identified

Mg abundances in these stars are significantly lower than expected

These stars may be helium-enriched red giants

Abstract

In this letter, the results of our low-resolution spectroscopic survey for identifying the hydrogen-deficient (H-deficient) stars in the red giant sample of the globular cluster Omega Cen are reported. Spectral analyses were carried out on the basis of the strengths of (0,0) MgH band and the Mg b triplet. In our sample, four giants were identified with weak/absent MgH bands in their observed spectra not as expected for their well determined stellar parameters. The Mg abundances for the program stars were determined from subordinate lines of the MgH band to the blue of the Mg b triplet, using the spectral synthesis technique. The derived Mg abundances for the program stars were as expected for the red giants of Omega Cen (Norris & Da Costa 1995), except for the four identified candidates. Determined Mg abundances of these four candidates are much lower than that expected for the red giants of Omega Cen, and are unacceptable based on the strengths of Mg b triplet in their observed spectra. Hence, the plausible reason for the weak/absent MgH bands in the observed spectra of these stars is a relatively lower abundance of hydrogen in their atmospheres. These giants may belong to the group of helium enriched red giants of Omega Cen.