The minimum Jeans mass, brown dwarf companion IMF, and predictions for detection of Y-type dwarfs
Abstract
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 (T_eff ⪉ 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{M}_J) 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{M}J to 79{M}_J) - the number of companion brown dwarfs is proportional to the mass to the -1.2±0.2 power.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- January 2009
- DOI:
- 10.1051/0004-6361:200810038
- arXiv:
- arXiv:0811.0429
- Bibcode:
- 2009A&A...493.1149Z
- Keywords:
-
- stars: planetary systems;
- stars: low-mass;
- brown dwarfs;
- Astrophysics
- E-Print:
- 6 pages, 2 figures, A&