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 K_s 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 25M_J (1 Gyr), 50M_J (solar age), and 60M_J (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.