The Cornell High-Order Adaptive Optics Survey for Brown Dwarfs in Stellar Systems. I. Observations, Data Reduction, and Detection Analyses

In this first of a two-paper sequence, we report techniques and results of the Cornell High-Order Adaptive Optics Survey (CHAOS) for brown dwarf companions. At the time of this writing, this study represents the most sensitive published population survey of brown dwarf companions to main-sequence stars for separations akin to our own outer solar system. The survey, conducted using the Palomar 200 inch (5 m) Hale Telescope, consists of Ks coronagraphic observations of 80 main-sequence stars out to 22 pc. At 1'' separation from a typical target system, the survey achieves median sensitivities 10 mag fainter than the parent star. In terms of companion mass, the survey achieves typical sensitivities of 25MJ (1 Gyr), 50MJ (solar age), and 60MJ (10 Gyr), using the evolutionary models of Baraffe and coworkers. Using common proper motion to distinguish companions from field stars, we find that no systems show positive evidence of a substellar companion (searchable separation ~1''-15''; projected separation ~10-155 AU at the median target distance). In the second paper of the series we will present our Monte Carlo population simulations.