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Published August 1, 2004 | Erratum + Submitted + Published
Journal Article Open

The Spectroscopically Determined Substellar Mass Function of the Orion Nebula Cluster


We present a spectroscopic study of candidate brown dwarf members of the Orion Nebula cluster (ONC). We obtained new J- and/or K-band spectra of ~100 objects within the ONC that are expected to be substellar on the basis of their K magnitudes and H-K colors. Spectral classification in the near-infrared of young low-mass objects is described, including the effects of surface gravity, veiling due to circumstellar material, and reddening. From our derived spectral types and existing near-infrared photometry, we construct an H-R diagram for the cluster. Masses are inferred for each object and used to derive the brown dwarf fraction and assess the mass function for the inner 5farcm1 × 5farcm1 of the ONC, down to ~0.02 M☉. The logarithmic mass function rises to a peak at ~0.2 M☉, similar to previous initial mass function determinations derived from purely photometric methods but falls off more sharply at the hydrogen-burning limit before leveling through the substellar regime. We compare the mass function derived here for the inner ONC with those presented in recent literature for the sparsely populated Taurus cloud members and the rich cluster IC 348. We find good agreement between the shapes and peak values of the ONC and IC 348 mass distributions but little similarity between the ONC and Taurus results.

Additional Information

© 2004. The American Astronomical Society. Received 2004 January 28 Accepted 2004 March 29 The authors would like to thank Davy Kirkpatrick for useful comments, which improved the final paper, and Kevin Luhman and Lee Hartmann for their insights and suggestions, which helped in our analysis. We thank Alice Shapley and Dawn Erb for sharing their method of subtracting sky lines from NIRSPEC images, as well as NIRSPEC support astronomers Greg Wirth, Grant Hill, and Paola Amico for their guidance during observing. We are also appreciative of Michael Meyer for his participation in the CRSP data acquisition and of assistance at the KPNO 4 m telescope from Dick Joyce. Finally, we thank LRIS observers N. Reid and B. Schaefer for obtaining several spectra for us. C. L. S. acknowledges support from a National Science Foundation Graduate Research Fellowship.

Attached Files

Published - Slesnick_2004_ApJ_610_1045.pdf

Submitted - 0404292.pdf

Erratum - Slesnick_2005_ApJ_625_1063.pdf


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