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 ofthe Cornell High-order Adaptive Optics Survey for brown dwarf companions(CHAOS). At the time of this writing, this study represents the most sensitivepublished population survey of brown dwarf companions to main sequence stars,for separation akin to our own outer solar system. The survey, conducted usingthe Palomar 200-inch Hale Telescope, consists of K-short coronagraphicobservations of 80 main sequence stars out to 22 parsecs. At 1 arcsecondseparations from a typical target system, the survey achieves mediansensitivities 10 magnitudes fainter than the parent star. In terms of companionmass, the survey achieves typical sensitivities of 25 Jupiter masses (1 Gyr),50 Jupiter masses (solar age), and 60 Jupiter masses (10 Gyr), usingevolutionary models of Baraffe et al. (2003). Using common proper motion todistinguish companions from field stars, we find that no systems show positiveevidence of a substellar companion (searchable separation 1-15 arcseconds[projected separation ~ 10-155 AU at the median target distance]). In thesecond paper of the series we shall present our Monte Carlo populationsimulations.Comment: Accepted by Astronomical Journal. Expected publication date: September 2005. Document has 24 pages including 5 figures and 3 table