E P ] 2 9 M ay 2 01 2 MOA 2010-BLG-477 Lb : constraining the mass of a microlensing planet from microlensing parallax , orbital motion and detection of blended light

Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA 2010-BLG477. The measured planet-star mass ratio is q = (2.181±0.004)×10−3 and the projected separation is s = 1.1228 ± 0.0006 in units of the Einstein radius. The angular Einstein radius is unusually large θE = 1.38 ± 0.11 mas. Combining this measurement with constraints on the “microlens parallax” and the lens flux, we can only limit the host mass to the range 0.13 < M/M⊙ < 1.0. In this particular case, the strong degeneracy between microlensing parallax and planet orbital motion prevents us from measuring more accurate host and planet masses. However, we find that adding Bayesian priors from two effects (Galactic model and Keplerian orbit) each independently favors the upper end of this mass range, yielding star and planet masses of M∗ = 0.67 +0.33 −0.13 M⊙ and mp = 1.5 +0.8 −0.3 MJUP at a distance of D = 2.3 ± 0.6 kpc, and with a semi-major axis of a = 2 −1 AU. Finally, we show that the lens mass can be determined from future high-resolution near-IR adaptive optics observations independently from two effects, photometric and astrometric. Subject headings: gravitational lensing: micro – planetary systems Institut d’Astrophysique et de Géophysique, Allée du 6 Août 17, Sart Tilman, Bât. B5c, 4000 Liège, Belgium Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road,Manchester, M13 9PL, UK Department of Physics, Sharif University of Technology, P. O. Box 11155–9161, Tehran, Iran Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany Astrophysics Research Institute, Liverpool John Moores University, Liverpool CH41 1LD, UK Department of Physics, Massachussets Institute of Technology, 77 Mass. Ave., Cambridge, MA 02139, USA McDonald Observatory, 16120 St Hwy Spur 78 #2, Fort Davis, Texas 79734, USA Department of Physics, University of Rijeka, Omladinska 14, 51000 Rijeka, Croatia Technische Universität Wien, Wieder Hauptst. 8-10, A-1040 Vienna, Austria Perth Observatory, Walnut Road, Bickley, Perth 6076, WA, Australia Royal Society University Research Fellow