Paper: astro-ph/0507416
Date: Mon, 18 Jul 2005 19:55:09 GMT (56kb)

Title: A Moving Cluster Distance to the Exoplanet 2M1207 B in the TW Hya
Association

Authors: Eric E. Mamajek
Comments: ApJ, in press
\\
A candidate extrasolar planet companion to the young brown dwarf 2MASSW
J1207334-393254 (2M1207) was recently discovered by Chauvin et al. They find
that 2M1207 B's temperature and luminosity are consistent with being a young,
\~5 M_Jupiter planet. The 2M1207 system is purported to be a member of the TW
Hya association (TWA), and situated ~70 pc away. Using a revised space motion
vector for TWA, and improved proper motion for 2M1207, I use the moving cluster
method to estimate the distance to the 2M1207 system and other TWA members. The
derived distance for 2M1207 (53+-6 pc) forces the brown dwarf and planet to be
half as luminous as previously thought. The inferred masses for 2M 1207 A and B
decrease to ~21 M_Jup and ~3-4 M_Jup, respectively, with the mass of B being
well below the observed tip of the planetary mass function and the theoretical
deuterium-burning limit. After removing probable Lower Centaurus-Crux (LCC)
members from the TWA sample, as well as the probable non-member TWA 22, the
remaining TWA members are found to have distances of 49 +- 3(s.e.m.) +-
12(1sigma) pc, and an internal 1D velocity dispersion of 0.8(+0.3,-0.2) km/s.
There is weak evidence that the TWA is expanding, and the data are consistent
with a lower limit on the expansion age of 10 Myr (95% confidence).

\\ ( http://arXiv.org/abs/astro-ph/0507416 , 56kb)