Red Be stars in the Magellanic Clouds?

Abstract

ABSTRACT We revisit the subject of Be candidate stars towards the Magellanic Clouds, previously studied by the authors using SPM4 proper motions. We obtain Gaia DR2 parallaxes and proper motions for 2357 and 994 LMC and SMC Be candidates, respectively. Parallaxes and proper motions versus colour V − I easily reveal the presence of the redder galactic contaminant foreground, as concluded in our previous work, but this time we do find a few red Be candidates consistent with being true Magellanic objects. A membership assessment to each Magellanic Cloud is done for each Be candidate, based on the distribution of their parallaxes and proper motions. From a compilation of published catalogues of spectroscopically confirmed emission line stars,we find that 41 (LMC) and 56 (SMC) of the Be candidates have shown the Hα line in emission. Near-infrared IRSF JHKs magnitudes are obtained for about 70 per cent of the Be candidates with Gaia DR2 astrometric data. Mid-infrared SAGE IRAC 3.6, 4.5, 5.8, and 8.0 $\mu$m magnitudes are obtained for about 85 per cent as well. After discarding possible Herbig Ae/Be stars, one LMC and three SMC B emission line confirmed stars show significantly redder optical, near- and mid-infrared colours than what has been typically measured for Classical Be stars – they are called red Be stars. Taking into account that classical Be stars do not show these red colours, further studies about these four stars are needed in order to establish their true nature and explain the observed red excess.