A search for HAeBe stars in the bar of the large magellanic cloud based on optical variability

Abstract

We searched the EROS1 database consisting of 80 000 stars in the bar of the Large Magellanic Cloud for blue objects with irregular photometric behavior similar to Galactic Herbig Ae/Be (HAeBe) stars. We found 14 new objects in addition to the discovery of 7 HAeBe candidate stars found in our previous studies. Based on their light curve and colours we classify these new objects also as EROS LMC HAeBe Candidates (ELHCs). The objects are located in an area of enhanced 60 μm emission, which indicates a star forming region. The stars are concentrated in three areas and the majority of the objects are clustered round the N 120 nebular complex. The light curves are interpreted with a simple model, involving obscuration by an inhomogeneous orbiting circumstellar dust cloud as the dominant cause of the variability. We find that the dust orbiting the stars is at a radial distance in the order of 10 to a few 100 AUs. Most of the objects are "bluer-when-fainter". This is attributed to the presence of a (blue) scattering nebula with a size smaller than the point spread function of the photometric images. The stellar parameters are derived from the photometry. The luminosity of the stars is in the range of 3.4 < 4.2 and the colours indicate spectral types O or B. The stars are located in the HR-diagram above the birthline for Galactic stars by about 1 dex in luminosity. The method used to detect the ELHCs stars on optical variability criteria is discussed. We show that our sample of HAeBe candidates in the EROS1 field of view is complete up to V ≃ 16.5m for the typical amplitude and time scale of the ELHCs.