Speaker: Victor Almendros (INAF)
Title: Evolution of the mass accretion rate and its relationship with the stellar and disk mass from brown dwarfs to stars
The time evolution of the dependence of the mass accretion rate with the stellar mass and the disk mass represents a fundamental way to understand the evolution of protoplanetary disks and the formation of planets. Recent studies suggest the existence of a bimodal accretion behavior at 2-3 Myr in the relationship of the stellar mass and the mass accretion rate, which may indicate that low-mass stars evolve faster (than higher-mass stars) into lower accretion rates. We recently measured the mass accretion rate of 26 new brown dwarfs and low-mass stars in the Ophiuchus, Cha-I and Upper Scorpius star-forming regions using X-Shooter/VLT. Combining these new observations with data from the literature, we compared the relations between accretion rate and stellar/disk properties of four different star-forming regions with different ages: Ophiuchus (1 Mar), Lupus (2 Myr), Cha-I (3 Myr) and Upper Scorpius (5-12 Myr). Overall, we observe hints of a faster evolution into low accretion rates of low-mass stars and brown dwarfs. At the same time, we also found that brown dwarfs present larger Mdisk/Macc ratios than stars in Ophiuchus, Lupus and Cha-I. This apparently contradictory result may imply that the evolution of protoplanetary disks around brown dwarfs may be different than in the stellar regime.