Abstract
We present the first trigonometric parallax and distance for a young planetary mass object. A likely TW Hya cluster member, 2MASSW J1207334-393254Ab (hereafter 2M1207Ab), is an M8 brown dwarf with a mid-to-late L-type planetary mass companion. Recent observations of spectral variability have uncovered clear signs of disk accretion and outflow, constraining the age of the system to <10 Myr. Because of its late spectral type and the clearly youthful nature of the system, 2M1207b is very likely a planetary mass object. We have measured the first accurate distance and luminosity for a self-luminous planetary mass object. Our parallax measurements are accurate to <2 mas (1 σ) for 2M1207Ab. With 11 total epochs of data taken from 2006 January through 2007 April (475 images for 2M1207Ab), we determine a distance of 58.8 ± 7.0 pc (17.0 mas, 1.28 σ) to 2M1207Ab and a calculated luminosity of (0.68-2.2) × 10-5 L☉ for 2M1207b. Hence, 2M1207Ab is a clear member of the TW Hya cluster in terms of its distance, proper motions, and youthful nature. However, as previously noted by Mohanty and coworkers, 2M1207b's luminosity appears low compared to its temperature according to evolutionary models.
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