2 00 8 ‘ Tail - end ’ Bondi - Hoyle Accretion in Young Star Clusters : Implications for Disks , Planets , and Stars Submitted to AJ , 7 - Nov - 2007

Young stars orbiting in the gravitational potential well of forming star clusters pass through the cluster’s dense molecular gas and can experience Bondi-Hoyle accretion from reservoirs outside their individual protostellar cloud cores. Accretion can occur for several million years after the stars form, but before the cluster disperses. This accretion is predominantly onto the disk and not the star. N-body simulations of stars orbiting in three young model clusters containing 30, 300, and 3000 stars are presented. The simulations include the gravitational potential of the molecular gas which smoothly disperses over time. The clusters have a star formation efficiency of 33% and a radius of 0.22 pc. We find that the disks surrounding solar-mass stars in the N=30 cluster accretes ∼ 0.01 M⊙ (1 minimum-mass solar nebula, MMSN) per Myr, with a 1σ width of 50 times due to variations in initial stellar positions and velocities within the cluster. The accretion rate scales as M2.1±0.1 for stars of mass M . The accretion rate is ∼ 5 times lower for N=3000 cluster, due to its higher stellar velocities and higher temperature. The Bondi-Hoyle accretion rates onto the disks are several times lower than accretion rates observed directly onto young stars (e.g., Muzerolle et al. 2005): these two accretion rates follow the same M behavior and may