Evolution of massive Be and Oe stars at low metallicity towards the Long Gamma Ray bursts\footnote{Based on ESO runs 069.D-0275(A), 072.D-0245(A) and (C).}

TL;DR

This study investigates how low metallicity environments like the SMC influence the evolution of massive Be/Oe stars and their potential as progenitors of long gamma-ray bursts, combining observations and models.

Contribution

It identifies low metallicity Be/Oe stars as potential long gamma-ray burst progenitors through observational data and theoretical modeling.

Findings

Be star occurrence in SMC is 3-5 times higher than in the Galaxy.

Low metallicity Be/Oe stars have high probabilities of being LGRB progenitors.

Comparison of models with observations supports the potential link.

Abstract

Several studies have shown recently that at low metallicity B-type stars rotate faster than in environments of high metallicity. This is a typical case in the SMC. As a consequence, it is expected that a larger number of fast rotators is found in the SMC than in the Galaxy, in particular a higher fraction of Be/Oe stars. Using the ESO-WFI in its slitless mode, the data from the SMC open clusters were examined and an occurrence of Be stars 3 to 5 times larger than in the Galaxy was found. The evolution of the angular rotational velocity at different metallicities seems to be the main key to understand the specific behavior and evolution of these stars. According to the results from this WFI study, the observational clues obtained from the SMC WR stars and massive stars, and the theoretical predictions of the characteristics must have the long gamma-ray burst progenitors, we have identified the low metallicity massive Be and Oe stars as potential LGRB progenitors. To this end, the ZAMS rotational velocities of the SMC Be/Oe stars were determined and compared to models. The expected rates and the numbers of LGRB were then calculated and compared to the observed ones. Thus, a high probability was found that low metallicity Be/Oe stars can be LGRB progenitors. In this document, we describe the different steps followed in these studies: determination of the number of Be/Oe stars at different metallicities, identification of the clues that lead to suppose the low metallicity Be/Oe stars as LGRB progenitors, comparison of models with observations.