Lupus-TR-3b: A Low-Mass Transiting Hot Jupiter in the Galactic Plane?

We present a strong case for a transiting Hot Jupiter planet identified during a single-field transit survey towards the Lupus Galactic plane. The object, Lupus-TR-3b, transits a V=17.4 K1V host star every 3.91405d. Spectroscopy and stellar colors indicate a host star with effective temperature 5000 ± 150K, with a stellar mass and radius of 0.87 ± 0.04M⊙ and 0.82 ± 0.05R⊙, respectively. Limb-darkened transit fitting yields a companion radius of 0.89 ± 0.07 RJ and an orbital inclination of 88.3 +1.3 −0.8 deg. Magellan 6.5m MIKE radial velocity measurements reveal a 2.4� K=114 ± 25m/s sinusoidal variation in phase with the transit ephemeris. The resulting mass is 0.81 ± 0.18MJ and density 1.4 ± 0.4g/cm 3 . Yband PANIC image deconvolution reveal a V>21 red neighbor 0.4 ′′ away which, although highly unlikely, we cannot conclusively rule out as a blended binary with current data. However, blend simulations show that only the most unusual binary system can reproduce our observations. This object is very likely a planet, detected from a highly efficient observational strategy. Lupus-TR-3b constitutes the faintest ground-based detection to date, and one of the lowest mass Hot Jupiters known. Subject headings: planetary systems: individual (Lupus-TR-3b) - techniques: photometric - techniques: radial velocities

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