Astronomy and Astrophysics, volume 493, 1149-1154 (2009/1-3)
The minimum jeans mass, brown dwarf companion IMF, and predictions for detection of y-type dwarfs.
ZUCKERMAN B. and SONG I.
Abstract (from CDS):
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 (Teff≲500K) 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 (∼13.5MJ) 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 <2Gyr 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 (13MJ to 79MJ) - the number of companion brown dwarfs is proportional to the mass to the -1.2±0.2 power.
stars: planetary systems - stars: low-mass, brown dwarfs