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Paper   IPM / Astronomy / 11834
School of Astronomy
  Title:   MOA-2009-BLG-387Lb: a massive planet orbiting an M dwarf
  Author(s):  Sohrab Rahvar
  Status:   To Appear
  Journal: Astronomy & Astrophysics
  Vol.:  529
  Pages:   16
  Publisher(s):   Astronomy & astrophysics
  Supported by:            IPM IPM
Aims. We report the discovery of a planet with a high planet-to-star mass ratio in the microlensing event MOA-2009-BLG-387, which exhibited pronounced deviations over a 12-day interval, one of the longest for any planetary event. The host is an M dwarf, with a mass in the range 0.07 M < Mhost < 0.49 M at 90best-estimated host mass, the planet mass is mp = 2.6 Jupiter masses for the median host mass, M = 0.19 M. Methods. The host mass is determined from two ?higher order? microlensing parameters. One of these, the angular Einstein radius #952;E = 0.31 � 0.03 mas has been accurately measured, but the other (the microlens parallax #960;E, which is due to the Earth?s orbital motion) is highly degenerate with the orbital motion of the planet. We statistically resolve the degeneracy between Earth and planet orbital effects by imposing priors from a Galactic model that specifies the positions and velocities of lenses and sources and a Kepler model of orbits. Results. The 902.7 AU, and 3.8 yr < P < 7.6 yr, respectively.

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