Cool Stars 14 - Submitted Abstract # 112
This version created on 05 October 2006

Brown-Dwarf Companions to Young Solar Analogs:  Frequency and
Properties


Stanimir Metchev, University of California, Los Angeles
Lynne Hillenbrand, California Institute of Technology

Direct imaging of sub-stellar companions to stars offers a unique
glimpse into the properties of wide (>5AU) low mass ratio (M2/M1<0.1)
systems, and a rare opportunity to determine age-dependent parameters
of brown dwarfs.  While a number of direct-imaging searches have met
with limited success over the past decade, the state of adaptive
optics technology on large telescopes is only now sufficiently mature
to allow the discovery of a significant population of
stellar/sub-stellar binaries.  We present updated results on wide
sub-stellar companions to stars from a survey of 101 young solar
analogs with high-order AO systems on 5-10m telescopes.  Because of
its large sample size and enhanced sensitivity, the survey offers a
more accurate estimate of the frequency of stellar/sub-stellar
binaries than has been possible to date.  Thus, we find that wide low
mass stellar and sub-stellar companions are derived from the same
initial mass function as their isolated counterparts.  Comparisons
with previous direct imaging surveys, which have focused primarily on
lower-mass and/or older primaries, allow a first glimpse into the age-
and mass-dependence of the frequency of low mass ratio binaries.  We
also discuss evidence for a surface gravity dependence of the
effective temperature near the L/T transition, based on the discovery
of an L7.5 companion to a 130-400  Myr-old star in our sample.  The
empirical characterization of the photospheres of similar young
ultra-cool dwarfs will be important for future direct-imaging studies
of extra-solar giant planets.

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