Cool Stars 14 - Submitted Abstract # 241
This version created on 05 October 2006

Gravity and Temperature Sensitive Features in the Near-IR Spectra of
Brown Dwarfs


Katelyn Allers, University of Hawaii
Michael Liu, University of Hawaii
Daniel Jaffe, University of Texas
Gregory Doppmann, NOAO-Tucson
Kevin Luhman, Penn State

Determining accurate masses of young brown dwarfs, as found by placing
them on an H-R diagram, has proven a difficult task.  Not only are the
evolutionary models untested in the low temperature/low gravity
regime, but the derived temperatures (from either model fits or from
the spectral types) of an object can vary by ~500  K depending on
which method is used (see recent work by Luhman et al., Close et al.,
Allers et al., and Jayawardhana & Ivanov).  Clearly, tighter
constraints on the gravities and temperatures of young brown dwarfs
are necessary to determine accurate masses.  We present R~1200-2000
near-IR spectra of a sample of young brown dwarfs in nearby
star-forming regions, with spectral types from M to early-L.
Comparing spectra of young brown dwarfs, field dwarfs, and giant
stars, we examine the gravity and temperature sensitivity of a variety
of atomic and molecular features.  We find an H-band H2O index capable
of determining spectral type to within one sub-type, independent of
gravity.  Based on our H2O index, we have designed a custom near-IR
filter, which in combination with broad-band J and H band filters, can
be used to determine the spectral type of M and L type objects.  We
also critically examine the H2O absorption induced shape of the H and
K bands and compare the gravity sensitivity of the continuum shape to
the gravities determined from atomic (Na and K) lines.

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