A SPECTROSCOPIC CENSUS IN YOUNG STELLAR REGIONS: THE σ ORIONIS CLUSTER

We present a spectroscopic survey of the stellar population of the s Orionis cluster. We have obtained spectral types for 340 stars. Spectroscopic data for spectral typing come from several spectrographs with similar spectroscopic coverage and resolution. More than half of the stars in our sample are members confirmed by the presence of lithium in absorption, strong H alpha in emission or weak gravity-sensitive features. In addition, we have obtained high-resolution (R similar to 34,000) spectra in the H alpha region for 169 stars in the region. Radial velocities were calculated from this data set. The radial velocity distribution for members of the cluster is in agreement with previous work. Analysis of the profile of the H alpha line and infrared observations reveals two binary systems or fast rotators that mimic the H alpha width expected in stars with accretion disks. On the other hand, there are stars with optically thick disks and narrow H alpha profiles not expected in stars with accretion disks. This contribution constitutes the largest homogeneous spectroscopic data set of the sigma Orionis cluster to date.