2001MNRAS.325.1441T

We present new high- and low-resolution spectroscopic and photometric data of nine members of the young association CMa R1. All the stars have circumstellar dust at some distance, as could be expected from their association with reflection nebulosity. Four stars (HD52721, HD53367, LkHα220 and LkHα218) show Hα emission and we argue that they are Herbig Be stars with discs. Our photometric and spectroscopic observations of these stars reveal new characteristics of their variability. We present first interpretations of the variability of HD52721, HD53367 and the two LkHα stars in terms of a partially eclipsing binary, a magnetic activity cycle and circumstellar dust variations, respectively. The remaining five stars show no clear indications of Hα emission in their spectra, although their spectral types and ages are comparable with those of HD52721 and HD53367. This indicates that the presence of a disc around a star in CMa R1 may depend on the environment of the star. In particular we find that all Hα emission stars are located at or outside the arc-shaped border of the Hii region, which suggests that the stars inside the arc have lost their discs through evaporation by UV photons from nearby O stars, or from the nearby (<25pc) supernova, about 1Myr ago.