  In this first of a two-paper sequence, we report techniques and results of
the Cornell High-order Adaptive Optics Survey for brown dwarf companions
(CHAOS). At the time of this writing, this study represents the most sensitive
published population survey of brown dwarf companions to main sequence stars,
for separation akin to our own outer solar system. The survey, conducted using
the Palomar 200-inch Hale Telescope, consists of K-short coronagraphic
observations of 80 main sequence stars out to 22 parsecs. At 1 arcsecond
separations from a typical target system, the survey achieves median
sensitivities 10 magnitudes fainter than the parent star. In terms of companion
mass, the survey achieves typical sensitivities of 25 Jupiter masses (1 Gyr),
50 Jupiter masses (solar age), and 60 Jupiter masses (10 Gyr), using
evolutionary models of Baraffe et al. (2003). 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 arcseconds
[projected separation ~ 10-155 AU at the median target distance]). In the
second paper of the series we shall present our Monte Carlo population
simulations.
