The PTF Orion Project: a Possible Planet Transiting a T-Tauri Star

We report observations of a possible young transiting planet orbiting a previously known weak-lined T-Tauri star in the 7-10Myr-old Orion-OB1a/25-Ori region. The candidate was found as part of the Palomar Transient Factory (PTF) Orion project. It has a photometric transit period of 0.448413 \pm 0.000040 days, and appears in both 2009 and 2010 PTF data. Follow-up low-precision radial velocity observations and adaptive-optics imaging suggest that the star is not an eclipsing binary, and that it is unlikely that a background source is blended with the target and mimicking the observed transit. Radial-velocity observations with the Hobby-Eberly and Keck telescopes yield a radial velocity that has the same period as the photometric event, but is offset in phase from the transit center by \approx -0.22 periods. The amplitude (half range) of the radial velocity variations is 2.4 km/s and is comparable with the expected radial velocity amplitude that stellar spots could induce. The radial velocity curve is likely dominated by stellar spot modulation and provides an upper limit to the projected companion mass of Mp sin iorb \leq 4.8\pm1.2 MJup; when combined with the orbital inclination, iorb, of the candidate planet from modeling of the transit lightcurve, we find an upper limit on the mass of the planetary candidate of Mp \leq 5.5\pm1.4 MJup. This limit implies that the planet is orbiting close to, if not inside, its Roche limiting orbital radius, so that it may be undergoing active mass loss and evaporating.

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