Spectroscopic properties of young stellar objects in the Lupus molecular clouds

Abstract

The results of an optical spectroscopic survey of a sample of young stellar objects (YSOs) and pre-main sequence (PMS) stars in the Lupus Clouds are presented. 92 objects were observed with VLT/FLAMES. All of those objects show IR 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 H-R diagrams for the population. The sample consists mostly of M-type stars, with 10% 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 ~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 IC348. The H{\alpha} line in emission, found in 49% of the sample, is used to distinguish between classical and weak-line T Tauri stars. 56% of the objects show H{\alpha} 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% of the H{\alpha} peak intensity. These mass accretion rates are, within a large scatter, consistent with the Mac \propto M 2 relation found in the literature.