Spectroscopic properties of young stellar objects in the Lupus molecular clouds

The results of an optical spectroscopic survey of a sample of young stellar objects and pre-main-sequence stars in the Lupus clouds are presented. 92 objects were observed with the Very Large Telescope/Fibre Large Array Multi Element Spectrograph. All of those objects show infrared excess as discovered by the Spitzer Legacy Program From Molecular Cores to Planet-Forming Disks (c2d). After reduction, 54 spectra with good signal-to-noise ratio are spectrally classified. Effective temperatures and luminosities are derived for these objects, and used to construct HertzsprungRussell diagrams for the population. The sample consists of mostly M-type stars, with 10 per cent K-type stars. Individual ages and masses are inferred for the objects according to theoretical evolutionary models. The mean population age is found to be between 3.6 and 4.4 Myr, depending on the model, while the mean mass is found to be similar to 0.3 M? for either model. Together with literature data, the distribution of spectral types is found to be similar to that in Chamaeleon I and IC 348. The Ha line in emission, found in 49 per cent of the sample, is used to distinguish between classical and weak-line T Tauri stars. 56 per cent of the objects show Ha in emission and are accreting T Tauri stars. Mass accretion rates between 10-8 and 10-11 M? yr-1 are determined from the full width at 10 per cent of the Ha peak intensity. These mass accretion rates are, within a large scatter, consistent with the relation found in the literature.