Joan Najita, National Optical Astronomy Observatories

From Stars to Super-planets: the Low-Mass IMF in the Young Cluster IC348

We investigate the low-mass population of the young cluster
IC348 down to the deuterium--burning limit, a fiducial boundary between
brown dwarf and planetary mass objects, using a new (HST/NICMOS
photometry-based) method for the spectral classification of late-type
objects.  Due to the efficiency of our spectral classification
technique, our study is complete to 0.015 Msun.  The mass function
derived for the cluster in this interval is similar to that of the
Pleiades, but appears significantly more abundant in brown dwarfs than
the mass function for companions to nearby sun-like stars.  This
provides compelling observational evidence for different formation and
evolutionary histories for substellar objects formed in isolation vs.
as companions.  Because our determination of the IMF is complete to
very low masses, we can place interesting constraints on the role of
physical processes such as fragmentation in the star and planet
formation process and the fraction of dark matter in the Galactic halo
that resides in substellar objects.