2001-2002 Colloquium Series
NAU Liberal Arts (Bldg 18, Rm 135), Monday, 1 April 2002, 4:00 PM
(Refreshments at 3:45 PM)
SEARCHING FOR GIANT PLANETS AROUND RED AND BROWN DWARFS
David Koerner , University of Pennsylvania.
Abstract
Direct detection of thermal emission from planetary-mass companions is
made feasible by searching around very faint dwarfs at infrared
wavelengths. Results are reported here for a Keck near infared imaging
survey of low-luminosity dwarfs (M6-L9) with masses at or below the
minimum-mass hydrogen-burning limit of 0.075 solar masses (corresponding
to ZAMS spectral type L3-L4). In a sample of 100 field dwarfs at
distances ranging from 10 to 60 pc, four substellar companions were
discovered with K-band brightness ratios near unity and separations near the
limit of resolution (0.2''-0.5'' corresponding to 5-10 AU). No companions
were detected at larger separations or with K-band brightness ratios
less than a half, despite sensitivity to objects more than 1000 times
fainter at separations between ten and several hundred AU. This suggests a
companion distribution for faint dwarf primaries that peaks at shorter
semi-major axes than for earlier type stars. High-contrast studies of the
companion population at subarcsecond separations poses observational
difficulties for imaging surveys but is amenable to investigation with
indirect methods such as astrometric and/or radial-velocity techniques.
Current ground-based parallax programs have the needed astrometric precision
(~1 mas) to identify substellar companions around M Dwarfs down to the
Deuterium-burning mass limit and beyond (13 Jupiter masses). A search strategy
is outlined which makes use of this capability and which comprises a
much-needed reconnaisance of potential targets for future planet searches
with ground- and space-based optical interferometry.
Local Host: Steve Tegler, (928) 523-9382.