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Brown Dwarf Companions to Young Solar Analogs - An Adaptive Optics Survey Using Palomar and Keck (Paperback)
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Brown Dwarf Companions to Young Solar Analogs - An Adaptive Optics Survey Using Palomar and Keck (Paperback)
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We present results from an adaptive optics survey conducted with
the Palomar and Keck telescopes over 3 years, which measured the
frequency of stellar and sub-stellar companions to Sun-like stars.
The survey sample contains 266 stars in the 3-10000 million year
age range at heliocentric distances between 8 and 200 parsecs and
with spectral types between F5-K5. A sub-sample of 101 stars,
between 3-500 million years old, were observed in deep exposures
with a coronagraph to search for faint sub-stellar companions. A
total of 288 candidate companions were discovered around the sample
stars, which were re-imaged at subsequent epochs to determine
physical association with the candidate host stars by checking for
common proper motion. Benefitting from a highly accurate
astrometric calibration of the observations, we were able to
successfully apply the common proper motion test in the majority of
the cases, including stars with proper motions as small as 20
milli-arcseconds/year. The results from the survey include the
discovery of three new brown dwarf companions (HD 49197B, HD
203030B, and ScoPMS 214B), 43 new stellar binaries, and a triple
system. The physical association of an additional, a
priori-suspected, candidate sub-stellar companion to the star HII
1348 is astrometrically confirmed. The newly-discovered and
confirmed young brown dwarf companions span a range of spectral
types between M5 and T0.5, and will be of prime significance for
constraining evolutionary models of young brown dwarfs and
extra-solar planets. Based on the 3 new detections of sub-stellar
companions in the 101 star sub-sample and following a careful
estimate of the survey incompleteness, a Bayesian
statisticalanalysis shows that the frequency of 0.012-0.072
solar-mass brown dwarfs in 30-1600 AU orbits around young solar
analogs is 6.8% (-4.9%, +8.3%; 2-sigma limits). While this is a
factor of 3 lower than the frequency of stellar companions to
G-dwarfs in the same orbital range, it is significantly higher than
the frequency of brown dwarfs in 0-3 AU orbits discovered through
precision radial velocity surveys. It is also fully consistent with
the observed frequency of 0-3 AU extra-solar planets. Thus, the
result demonstrates that the radial-velocity "brown dwarf desert"
does not extend to wide separations, contrary to previous belief.
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