Variability of B and Be stars in the LMC/SMC: binaries and pulsations

TL;DR

This study investigates the variability, binarity, and pulsations of B and Be stars in the Magellanic Clouds, revealing new pulsating stars in low-metallicity environments and analyzing their properties compared to the Milky Way.

Contribution

It provides the first identification of multiperiodic B and Be stars in the SMC and compares binary ratios and pulsation characteristics across different metallicities.

Findings

Discovered the first multiperiodic B and Be stars in the SMC.

Found that pulsation instability strips are shifted towards higher temperatures in the SMC.

More pulsating Be stars than B stars in the SMC, suggesting rotation influences pulsations.

Abstract

To study the variability of the 523 B and Be stars observed in the Magellanic clouds with the VLT-FLAMES, we cross-matched the stars of our sample with the photometric database MACHO, which provides for each star an 8 years lightcurve. We searched for long, medium, and short-term periodicity and found the eclipsing binaries in our sample. For these stars, combining, spectroscopy and photometry, we were able to provide information on several systems of stars (systemic velocities, ratios of masses, etc). We also present the ratios of B-binaries to B-non binaries in the LMC/SMC in comparison with the MW. Note that this ratio is also an important issue to understand the mechanism of star-formation at low metallicity. We also found the first multiperiodic B and Be stars in the SMC, in particular the first SMC Beta Cep and SPB, while, according to the models, pulsations were not foreseen in low metallicity environments, i.e. typically in the SMC. Our results show that the instability strips are shifted towards higher temperatures in comparison with the Milky Way' strips of pulsating B-type stars. By the fact that we found more pulsating Be stars than pulsating B stars in the SMC, it seems that the fast rotation favours the presence of pulsations. However, the ratio of pulsating B-type stars to "non"-pulsating B-type stars at low metallicity is lower than at high metallicity.