1999A&A...341..827L

We report the serendipitous discovery of seven luminous irregular variables in the LMC by the EROS project. The stars have V≃15mag to 17mag, (B_E-R_E)≃0mag, and vary by about 0.4mag on timescales of 10 to 40 days. The variations in B_E and R_E are about equal but the stars are slightly bluer when they are fainter. Medium resolution optical spectra show strong Hα emission, weak Hβ emission and absorption lines of the higher Balmer lines. Absorption lines of He I, C III, O II and Si IV are present in the spectra of some of the stars. The spectral types derived from the presence or absence of the lines are between late-O and late-B. Effective temperatures and luminosities were derived from the energy distributions and independently from the EROS photometry combined with the approximate spectral types. The luminosity, derived from V, E(B-V), and the distance of the LMC, are in the range of 10³ to 10⁴L_☉. The strong Hα emission, the spectral types, the luminosities and the irregular variations are similar (but not the same) to those of the Galactic pre-main sequence HAeBe stars (i.e. the Herbig Ae/Be stars). However the stars are about a factor 10 more luminous than the luminosity upper limit for Galactic HAeBe stars. This might be due to a shorter accretion timescale (τ_accr=M_*/{dot}(M)), or to the smaller dust-to-gas ratio in the LMC.