HST/NICMOS III imaging in Orion Nebula Cluster

The main aim is to determine the ratio of low-mass stars to brown dwarfs for the cluster as a function of radius out to a radial distance of 1.5pc. The sensitivity of the data outside the nebulous central region is F160W<=21.0mag, significantly deeper than previous studies of the region over a comparable area.

We create an extinction limited sample and determine the ratio of low-mass stars (0.08-1M_{sun}_) to brown dwarfs (0.02-0.08M_{sun}_ and 0.03-0.08M_{sun}_) for the cluster as a whole and for several annuli. The ratio found for the cluster within a radius of 1.5pc is R_02_=N(0.08-1M_{sun}_)/N(0.02-0.08M_{sun}_)=1.7+/-0.2, and R_03_=N(0.08-1M_{sun}_)/N(0.03-0.08M_{sun}_)=2.4+/-0.2, after correcting for field stars. The ratio for the central 0.3x0.3pc^2^ region down to 0.03M_{sun}_ was previously found to be R_03_=3.3^+0.8^_-0.7_, suggesting the low-mass content of the cluster is mass segregated.