Blue irregular variable stars in the Small Magellanic Cloud from EROS2 : Herbig Ae/Be or classical Be stars ?

Abstract

Using data from the EROS2 microlensing survey, we report the discovery of two blue objects with irregular photometric behaviour of $ΔV \sim 0.1$-0.4 mag on time scales of 20 to 200 days. They show a bluer when fainter behaviour. Subsequent spectra taken with the ESO 3.6m telescope show spectral type B4eIII and B2eIV-V with strong $H α$ emission. These objects resemble the Herbig AeBe but also classical Be stars. At this stage, it is not possible to distinguish unambiguously between pre-main sequence and classical Be nature. If we favour the pre-main sequence interpretation, they are more luminous than the luminosity upper limit for Galactic HAeBe stars. The same was found for the HAeBe candidates in the LMC. This might be due to a shorter accretion time scale ($τ= M_*/\dot{M}$), or the smaller dust content during the pre-main sequence evolution of SMC and LMC stars.