The stellar mass-accretion rate relation in T Tauri stars and brown dwarfs

Recent observations show a strong correlation between stellar mass and accretion rate in young stellar and substellar objects, with the scaling M-acc proportional to M-double dagger(2) holding over more than 4 orders of magnitude in accretion rate. We explore the consequences of this correlation in the context of disk evolution models. We note that such a correlation is not expected to arise from variations in disk angular momentum transport efficiency with stellar mass, and we suggest that it may reflect a systematic trend in disk initial conditions. In this case we find that brown dwarf disks initially have rather larger radii than those around more massive objects. By considering disk evolution, and invoking a simple parameterization for a shutoff in accretion at the end of the disk lifetime, we show that such models predict that the scatter in the stellar mass-accretion rate relationship should increase with increasing stellar mass, in rough agreement with current observations.