We present an analysis of NICMOS photometry and low-resolution grism spectroscopy of low-mass stars and sub-stellar objects in the young star-forming region NGC 1333 .
Our goal is to constrain the ratio of low-mass stars to sub-stellar objects down to 20 M _ { Jup } in the cluster as well as constrain the cluster IMF down to 30 M _ { Jup } in combination with a previous survey of NGC 1333 by Wilking et al .
Our survey covers 4 fields of 51.2 ” x 51.2 ” , centered on brown dwarf candidates previously identified in Wilking et al .
We extend previous work based on the use of a water vapor index for spectral typing to wavelengths accessible with NICMOS on the HST .
Spectral types were derived for the 14 brightest objects in our fields , ranging from \leq M0 - M8 , which at the age of the cluster ( 0.3 Myr ) corresponds to a range in mass of \geq 0.25 - 0.02 M _ { \odot } .
In addition to the spectra , we present an analysis of the color-magnitude diagram using pre-main sequence evolutionary models of D ’ Antona & Mazzitelli .
Using an extinction-limited sample , we derive the ratio of low-mass stars to brown dwarfs .
Comparisons of the observed ratio to that expected from the field IMF of Chabrier indicate that the two results are consistent .
We combine our data with that of Wilking et al .
to compute the ratio of intermediate-mass stars ( 0.1 - 1.0 M _ { \odot } ) to low-mass objects ( 0.03 - 0.1 M _ { \odot } ) in the cluster .
We also report the discovery of a faint companion to the previously confirmed brown dwarf ASR 28 , as well as a possible outflow surrounding ASR 16 .
If the faint companion is confirmed as a cluster member , it would have a mass of \approx 5 M _ { Jup } ( mass ratio 0.15 ) at a projected distance of 350 AU , similar to 2MASS 1207-3923 B .