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L. Hillenbrand, J. Carpenter (Caltech)
Star-forming regions are advantageous for studies of the stellar initial mass function since neither stellar nor dynamical evolution has had time to deplete the population. Furthermore, at very young ages (~1 Myr), contracting pre-main sequence stars of low mass are 2-3.5 orders of magnitude more luminous than their counterparts on the main sequence. To continue our previous work on the initial mass function in the Orion Nebula Cluster, we present results from 0.4-0.7" FWHM imaging at the near-infrared K (2.2\mum), H (1.6\mum), and Z (1.0\mum) bands over a 5.3\times5.3 arcmin2 area centered on \theta1C Ori. Our photometry is complete for source detection at the 20\sigma level to K\approx17 mag and thus our survey is sensitive to objects as low-mass as 0.02M\odot seen through visual extinction values as high as 10 magnitudes. Consistent with previous literature, we find a peak in the magnitude distribution at K\approx12.5 mag with a steady decline in the source counts to our completeness limit. We use the observed magnitudes, colors, and star counts to constrain the shape of the initial mass function across the hydrogen-burning limit. We compare our results with those previously obtained by us using less complete optical photometry and spectroscopy.
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