标题： 飞马座TW星协中系外行星2M1207 B的视差距离 显示英文标题

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

摘要： 一颗候选的太阳系外行星 companions 是年轻的褐矮星 2MASSW J1207334-393254 (2M1207)，最近由 Chauvin 等人发现。 他们发现 2M1207 B 的温度和光度与一颗年轻的、约 5 倍木星质量的行星一致。 2M1207 系统据称是 TW Hya 协会 (TWA) 的成员之一，并且距离地球约 70 秒差距。 使用修订后的 TWA 空间运动向量和改进的 2M1207 视差运动，我用移动星团法估计了 2M1207 系统和其他 TWA 成员的距离。 得出的 2M1207 距离（53±6 秒差距）迫使这个褐矮星和行星比之前认为的亮度降低了一半。 推断出的 2M1207 A 和 B 的质量分别减少到约 21 倍木星质量和 3-4 倍木星质量，其中 B 的质量明显低于观测到的行星质量函数的上限和理论氘燃烧极限。 在从 TWA 样本中去除可能的 Lower Centaurus-Crux (LCC) 成员以及可能的非成员 TWA 22 后，剩余的 TWA 成员距离为 49 ± 3（标准误差）± 12（1σ）秒差距，内部一维速度弥散度为 0.8(+0.3,-0.2) 公里/秒。 有弱证据表明 TWA 正在膨胀，数据支持其膨胀年龄下限为 10 百万年（95% 置信度）。 显示英文摘要

摘要： 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).