Issue |
A&A
Volume 493, Number 3, January III 2009
|
|
---|---|---|
Page(s) | 1149 - 1154 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361:200810038 | |
Published online | 20 November 2008 |
The minimum Jeans mass, brown dwarf companion IMF, and predictions for detection of Y-type dwarfs
1
Dept. of Physics & Astronomy and Center for Astrobiology, University of California, Los Angeles, 475 Portola Plaza, Los Angeles, CA 90095–1547, USA e-mail: ben@astro.ucla.edu
2
Department of Physics & Astronomy, The University of Georgia, Athens, GA 30605, USA e-mail: song@physast.uga.edu
Received:
23
April
2008
Accepted:
14
November
2008
Cool L- and T-type objects were discovered first as companions to
stars in 1988 and 1995, respectively. A certain example of the even
cooler Y-type spectral class ( 500 K) has not been
seen. Recent infrared-imaging observations of stars and brown dwarfs
indicate that substellar companions with large semi-major axes and
with masses less than the brown dwarf/giant planet dividing line
(~13.5
) are rare. Theoretical considerations of the Jeans
mass fragmentation of molecular clouds are consistent with this
minimum mass cutoff and also with the semi-major axis (hundreds of AU)
characteristic of the lowest mass imaged companions. As a consequence,
Y-class companions with large semi-major axes should be scarce around
stars <2 Gyr old, and also around substellar primaries of all ages.
By focusing on brown dwarf companions to young stellar primaries, it
is possible to derive a first estimate of the brown dwarf IMF over the
entire range of brown dwarf masses (13
to 79
) – the number
of companion brown dwarfs is proportional to the mass to the
-1.2±0.2 power.
Key words: stars: planetary systems / stars: low-mass, brown dwarfs
© ESO, 2009
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