Cool Stars 14 - Submitted Abstract # 383
This version created on 11 October 2006

The very nearby M/T dwarf binary SCR 1845-6357


Markus Kasper, ESO
Beth Biller, Steward Observatory 
Wolfgang Brandner, MPIA 
Laird Close, Steward Observatory

The recently discovered very nearby star SCR 1845-6357
(hereafter SCR 1845) is the first late M/T dwarf binary
discovered and a rare example of a system  containing a brown
dwarf companion in the heart of the brown dwarf desert. We 
present spatially resolved VLT/NACO images and low resolution
spectra of SCR  1845 in the J, H and K near-infrared bands.
Since the T dwarf companion, SCR  1845B, is so close to the
primary SCR 1845A (currently 4 AU), orbital motion is  evident
even within a year. Following the orbital motion, the binary's
mass can  be measured accurately within a decade, making SCR
1845B a key T-dwarf mass-luminosity calibrator. The NIR spectra
allow for accurate determination of spectral type and also for
rough estimates of the object's physical parameters.  Our data
prove that SCR1845B is a T6 dwarf that is gravitationally bound
to the M8.5 primary with an orbital period of about 30 years.
By comparison to theoretical models, the observed suppression
of K-band flux indicates high surface gravity and/or low
metallicity. 

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