A moving cluster distance to the exoplanet 2M1207b in the TW Hydrae association

A candidate extrasolar planet companion to the young brown dwarf 2MASSW J1207334 - 393254 ( hereafter 2M1207) was recently discovered by Chauvin et al. They find that the temperature and luminosity of 2M1207b are consistent with a young, similar to 5MJ planet. The 2M1207 system is purported to be a member of the TW Hya association (TWA) and situated similar to 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 2M1207A and 2M1207b decrease to similar to 21 and similar to 3 - 4M(J), respectively, with the mass of 2M1207b 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 nonmember TWA22, the remaining TWA membership is found to have distances of 49 - 3 ( s: e: m:) +/- 12 ( 1 sigma) pc and an internal one-dimensional velocity dispersion of 0.8(-0.2)(+0.3) km s(-1). 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).