The Cornell High-Order Adaptive Optics Survey for brown dwarfs in stellar systems. II. Results from Monte Carlo population analyses

In this second of a two-paper sequence, we present Monte Carlo population simulation results of brown dwarf companion data collected during the Cornell High-Order Adaptive Optics Survey (CHAOS) for brown dwarf companions. Making reasonable assumptions of orbital parameters (random inclination, random eccentricity, and random longitude of pericenter) and age distributions and using published mass functions, we find that the brown dwarf companion fraction around main-sequence stars is 0.0%-9.3% for the 25-100 AU semimajor axis region. We find a corresponding L dwarf companion fraction of 0.0%-3.3%. We compare our population analysis methods and results with techniques and results presented by several other groups. In this comparison we discover that systematic errors (most notably resulting from orbital projection effects) occur in the majority of previously published brown dwarf companion population estimates, leading authors to claim results not supported by the observational data.