The stellar composition of the star formation region CMa R1-II. Spectroscopic and photometric observations of nine young stars

We present new high- and low-resolution spectroscopic and photometric data of nine members of the young association CMa R1. All the stars have circums tellar dust at some distance, as could be expected from their association w ith reflection nebulosity. Four stars (HD 52721, HD 53367, LkH alpha 220 an d LkH alpha 218) show H alpha 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 int erpretations of the variability of HD 52721, HD 53367 and the two LkH alpha stars in terms of a partially eclipsing binary, a magnetic activity cycle and circumstellar dust variations, respectively. The remaining five stars s how no clear indications of H alpha emission in their spectra, although the ir 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 Rt may de pend on the environment of the star. In particular we find that all Ha emis sion stars are located at or outside the arc-shaped border of the H it regi on, which suggests that the stars inside the arc have lost their discs thro ugh evaporation by UV photons from nearby O stars, or from the nearby (< 25 pc) supernova, about 1 Myr ago.