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C. L. Slesnick, L. A. Hillenbrand, J. M. Carpenter (Caltech)
We present the results of a near-infrared spectroscopic study of sub-stellar objects in the Orion Nebula Cluster (ONC). In star forming regions like the ONC, low-mass pre-main-sequence stars and brown dwarfs are 2-3.5 orders of magnitude more luminous than their counterparts on the main sequence. At the age (1-2 Myr) and distance (~460 pc) of the ONC, the hydrogen-burning limit occurs at K~13.5. Therefore, such regions provide the best opportunities for studying the shape of the initial mass function (IMF) into the brown dwarf regime.
R~1400 observations of >45 objects were obtained with NIRSPEC on Keck II (Mauna Kea, Hawaii). Targets were selected from the imaging survey by Hillenbrand & Carpenter (2000) which used observed (H-K) colors and K magnitudes to constrain the shape of the sub-stellar IMF in the ONC. Spectroscopic observations offer a means for more accurate assessment of membership and foreground extinction, leading to a more precise measurement of the IMF. We have constructed indices in the J-band and K-band to measure the strength of water and iron hydride molecular features which we find to be excellent indicators of temperature. Surface gravity is determined from the relative depths of KI absorption lines. The Keck spectra confirm that most of the sources have late spectral types consistent with young brown dwarfs.
The author(s) of this abstract have provided an email address for comments about the abstract: cls@astro.caltech.edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.