Early Evolution of Stellar Groups and Clusters: Environmental Effects on Forming Planetary Systems

This paper studies the dynamical evolution of young stellar clusters with $N$= 100 - 1000 members. We use N-body simulations to explore how evolutiondepends on system size $N$ and the initial conditions. Motivated by recentobservations of extremely young systems, this study compares subvirial andvirial starting states. Multiple realizations of equivalent cases (100simulations per case) are used to build up a robust statistical description ofthese systems, e.g., distributions of closest approaches, mass profiles, anddistributions of radial locations. These results provide a framework from whichto assess the effects of these clusters on star and planet formation. Thedistributions of radial positions are used in conjunction with distributions ofFUV luminosities (also calculated here) to determine the radiation exposure ofcircumstellar disks. The distributions of closest approaches are used inconjunction with scattering cross sections (calculated here from $10^5$scattering experiments) to determine the probability of solar systemdisruption. We also use the nearby cluster NGC 1333 as a test case. Our mainconclusion is that clusters in this size range have only a modest effect onforming planetary systems: Interaction rates are low so that the typical solarsystem experiences a single encounter within 1000 AU. Radiation exposure islow, with median FUV flux $G_0$ = 900, so that photoevaporation of disks isonly important beyond 30 AU. Given the low interaction rates and modestradiation levels, we suggest that solar system disruption is a rare event inthese clusters.Comment: 54 pages; accepted to Ap