Cool Stars 14 - Submitted Abstract # 230
This version created on 05 October 2006

Accurate Mass Determination of Young Low Mass Objects with Theoretical
Evolutionary Tracks


Laird M. Close
Niranjan Thatte
Eric L. Nielsen
Roberto Abuter
Fraser Clarke
Matthias Tecza

It is currently very challenging to determine masses (and their
uncertainties) from the evolutionary models of young cool (low-mass)
objects.  We review all known calibrators with known dynamical masses,
and compare them to a popular set evolutionary VLM and brown dwarf
tracks.  In particular, we present new photometric and spectroscopic
measurements for the unique, young, low-mass evolutionary track
calibrator AB Dor C.  While the new Ks photometry is similar to that
previously published in Close et al.  (2005) the spectral type is
found to be much earlier.  Based on a new (much improved) H & K IFS
spectra of AB Dor C (Thatte et al.  2006) we adopt a spectral type of
M5.5+/-1 for AB Dor C.  We also present new astrometry for the system
which further supports a 0.090+/-0.005 Msun mass for the system.  Once
armed with an accurate spectrum and Ks flux we find L=0.0021+/-0.0005
Lsun and Teff=2925+/-150K for AB Dor C.  These values are consistent
with a ~75 Myr 0.090+/-0.005 Msun object like AB Dor C according to
the DUSTY evolutionary tracks (Chabrier et al.  2000).  Hence masses
can be estimated from the HR diagram with the DUSTY tracks for young,
low-mass, objects like AB Dor C.  However, we cautiously note that
underestimates of the mass from the tracks can occur if one lacks a
proper (continuum preserved) spectra and/or is relying on J and H
fluxes alone.

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