Hubble Space Telescope NICMOS observations of the embedded cluster in NGC 2024:: Constraints on the initial mass function and binary fraction

We present an analysis of NICMOS observations of the embedded cluster associated with NGC 2024. An analysis of the cluster color-magnitude diagram (CMD) using the models of D'Antona & Mazzitelli and Bara. e et al. (published in 1997 and 1998, respectively) indicates that the ratio of intermediate-mass (1.0-10.0 M-circle dot) to low-mass (0.1-1.0 M-circle dot) stars is consistent with the stellar initial mass function (IMF) for the field. In addition to the CMD analysis, we present results on the multiplicity of stars in the region. Three companions (in a sample of 95 potential primaries) were found, with angular separations between 0."4 and 1."0, translating to a projected linear separation of 184-460 AU for an estimated distance of 460 pc. The completeness of binary detections is assessed using recovery fractions calculated by a series of tests using artificially generated companions to potential primaries in the data frames. We find that the binary fraction in NGC 2024 is consistent with that of Duquennoy & Mayor (published in 1991) for solar neighborhood stars over the range of separations and companion masses appropriate for our survey.