Be stars and binaries in the field of the SMC open cluster NGC330 with VLT-FLAMES

TL;DR

This study investigates the properties, binary status, and variability of Be stars in the low-metallicity environment of the SMC-NGC330 cluster using VLT-FLAMES data, revealing higher Be star proportions and multiple variability periods.

Contribution

It provides new spectroscopic and photometric analysis of Be stars in the SMC, including binary detection and variability characterization, in a low-metallicity context.

Findings

Higher proportion of early Be stars with strong Halpha emission in SMC

Slight increase in Be/B star ratio with decreasing metallicity

Identification of spectroscopic and photometric binaries and their periods

Abstract

Observations of hot stars belonging to the young cluster SMC-NGC330 and its surrounding region were obtained with the VLT-GIRAFFE facilities in MEDUSA mode. We investigated the B and Be star properties and proportions in this environment of low metallicity. We also searched for rapid variability in Be stars using photometric databases. With spectroscopic measurements we characterized the emission and properties of Be stars. By cross-correlation with photometric databases such as MACHO and OGLE, we searched for binaries in our sample of hot stars, as well as for short-term variability in Be stars. We report on the global characteristics of the Be star sample (131 objects). We find that the proportion of early Be stars with a large equivalent width of the Halpha emission line is higher in the SMC than in the LMC and MW. We find a slight increase in the proportion of Be stars compared to B-type stars with decreasing metallicity. We also discovered spectroscopic and photometric binaries, and for the latter we give their orbital period. We identify 13 Be stars with short-term variability. We determine their period(s) and find that 9 Be stars are multiperiodic.