Photometric determination of the mass accretion rates of pre-mainsequence stars - III. Results in the Large Magellanic Cloud

Abstract

We present a multi-wavelength study of three star forming regions, spanning the age range 1-14 Myr, located between the 30 Doradus complex and supernova SN1987A in the Large Magellanic Cloud (LMC). We reliably identify about 1000 pre-main sequence (PMS) star candidates actively undergoing mass accretion and estimate their stellar properties and mass accretion rate (Macc). Our measurements represent the largest Macc dataset of low-metallicity stars presented so far. As such, they offer a unique opportunity to study on a statistical basis the mass accretion process in the LMC and, more in general, the evolution of the mass accretion process around low-metallicity stars. We find that the typical \dot{M} of PMS stars in the LMC is higher than for galactic PMS stars of the same mass, independently of their age. Taking into account the caveats of isochronal age and \dot{M} estimates, the difference in Macc between the LMC and our Galaxy appears to be about an order of magnitude. We review the main mechanisms of disk dispersal and find indications that typically higher Macc are to be expected in low-metallicity environments. However, many issues of this scenario need to be clarified by future observations and modeling. We also find that, in the mass range 1-2 M_sun, the Macc of PMS stars in the LMC increases with stellar mass as \dot{M}acc\proptoM^b, with b \approx1, i.e. slower than the second power low found for galactic PMS stars in the same mass regime.