2012A&A...547A.104B

Knowledge of radial velocities, elemental abundances, and accretion properties of members of star-forming regions is important for our understanding of stellar and planetary formation. While infrared observations reveal the evolutionary status of the disk, optical spectroscopy is fundamental to acquire information on the properties of the central star and on the accretion characteristics. Existing 2MASS archive data and the Spitzer c2d survey of the ChamaeleonII dark cloud have provided disk properties of a large number of young stars. We complement these data with optical spectroscopy with the aim of providing physical stellar parameters and accretion properties. We use FLAMES/UVES and FLAMES/GIRAFFE spectroscopic observations of 40 members of the ChamaeleonII star-forming region to measure radial velocities through cross-correlation technique, lithium abundances by means of curves of growth, and for a suitable star elemental abundances of Fe, Al, Si, Ca, Ti, and Ni using the code MOOG. From the equivalent widths of the Hα, Hβ, and the HeI λ5876, λ6678, λ7065Å emission lines, we estimate the mass accretion rates, {dot}(M)_acc, for all the objects. We derive a radial velocity distribution for the ChamaeleonII stars, which is peaked at <V_rad≥11.4±2.0k/s. We find dependencies of {dot}(M)_acc∝M_*^1.3 and of {dot}(M)_acc∝Age^–0.82 in the ∼0.1-1.0M_☉ mass regime, as well as a mean mass accretion rate for Chamaeleon II of {dot}(M)_acc∼7⁺²⁶_–5x10^–10M_☉/yr. We also establish a relationship between the HeI λ7065Å line emission and the accretion luminosity. The radial velocity distributions of stars and gas in ChamaeleonII are consistent. The spread in {dot}(M)_acc at a given stellar mass is about one order of magnitude and can not be ascribed entirely to short timescale variability. Analyzing the relation between {dot}(M)_acc and the colors in Spitzer c2d and 2MASS bands, we find indications that the inner disk changes from optically thick to optically thin at {dot}(M)_acc∼10^–10M_☉/yr. Finally, the disk fraction is consistent with the age of ChamaeleonII.