Encounter-triggered Disk Mass Loss in the Orion Nebula Cluster

The relevance of encounters on the destruction of protoplanetary disks in the Orion Nebula cluster (ONC) is investigated by combining two different types of numerical simulation. First, star-cluster simulations are performed to model the stellar dynamics of the ONC, the results of which are used to investigate the frequency of encounters, the mass ratio and separation of the stars involved, and the eccentricity of the encounter orbits. The results show that interactions that could influence the star-surrounding disk are more frequent than previously assumed in the core of the ONC, the so-called Trapezium cluster. Second, a parameter study of star-disk encounters is performed to determine the upper limits of the mass loss of the disks in encounters. For simulation times of ~1-2 Myr (the likely age of the ONC) the results show that gravitational interaction might account for a significant disk mass loss in dense clusters. Disk destruction is dominated by encounters with high-mass stars, especially in the Trapezium cluster, where the fraction of disks destroyed due to stellar encounters can reach 10%-15%. These estimates are in accord with recent observations of Lada et al., who determined a stellar disk fraction of 80%-85%. Thus, it is shown that in the ONC—a typical star-forming region—stellar encounters do have a significant effect on the mass of protoplanetary disks and thus affect the formation of planetary systems.