Cool Stars 14 - Submitted Abstract # 262
This version created on 05 October 2006

Preliminary Orbit and Masses of the Nearby Binary L Dwarf GJ 1001BC


David Golimowski, Johns Hopkins University
Dante Minniti, Pontificia Universidad Catolica de Chile
Todd Henry, Georgia State University
Holland Ford, Johns Hopkins University

We present the preliminary results of a continuing VLT program to map
the orbit of the nearby binary L4.5 dwarf GJ 1001BC (LHS 102BC).
Since discovering its duplicity in 2002 and 2003 using HST's NICMOS
and ACS, we have obtained high-resolution images of GJ 1001BC at five
epochs between October 2004 and September 2006 using the NAOS/CONICA
system at VLT-UT4 (Yepun).  Our HST and VLT images span nearly one
complete 4 year orbit.  A least-squares fit of a Keplerian orbit from
October 2002 to November 2005 yields a combined binary mass of 0.100
± 0.026 M_sun for a new parallactic distance measurement of 13.0  ±
0.7 pc to the M dwarf GJ 1001A.  Hypothetically assuming a 3:2 mass
ratio for the nearly equal-luminosity L dwarfs, we estimate masses of
0.060  ± 0.016 M_sun and 0.040  ± 0.010  M_sun for GJ 1001B and C,
respectively.  If these preliminary values are sustained by our
continuing orbit and parallax measurements, then GJ 1001C will be the
least massive L dwarf for which a dynamical mass has been measured.

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