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Abstract
Aims. We report the discovery of a planet with a high planettostar mass ratio in the microlensing event MOA2009BLG387, which exhibited pronounced deviations over a 12day interval, one of the longest for any planetary event. The host is an M dwarf, with a mass in the range 0.07 Mcircle dot < Mhost < 0.49 Mcircle dot at 90% confidence. The planetstar mass ratio q = 0.0132 +/ 0.003 has been measured extremely well, so at the bestestimated host mass, the planet mass is m(p) = 2.6 Jupiter masses for the median host mass, M = 0.19 Mcircle dot.
Methods. The host mass is determined from two "higher order" microlensing parameters. One of these, the angular Einstein radius theta(E) = 0.31 +/ 0.03 mas has been accurately measured, but the other (the microlens parallax pi(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 90% confidence intervals for the distance, semimajor axis, and period of the planet are 3.5 kpc < DL < 7.9 kpc, 1.1 AU < a < 2.7 AU, and 3.8 yr < P < 7.6 yr, respectively.
Original language  English 

Article number  A102 
Number of pages  16 
Journal  Astronomy & Astrophysics 
Volume  529 
DOIs  
Publication status  Published  May 2011 
Keywords
 gravitational lensing: micro
 methods: data analysis
 planets and satellites: detection
 methods: numerical
 instrumentation: adaptive optics
 instrumentation: photometers
 GALACTIC BULGE
 MICROLENSING EVENT
 JUPITER/SATURN ANALOG
 GIANT PLANETS
 SNOW LINE
 STARS
 MASSES
 PHOTOMETRY
 COOL
 LUMINOSITY
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Astrophysics in St Andrews: Astrophysics in St Andrews / SUPA (Continuan of Rolling Grant  XPP089
Bonnell, I. A. (PI), Cameron, A. C. (CoI), Dominik, M. (CoI), Driver, S. P. (CoI), Greaves, J. S. (CoI), Horne, K. D. (CoI), Jardine, M. M. (CoI), Wood, K. (CoI) & Zhao, H. (CoI)
Science & Technology Facilities Council
1/04/09 → 31/03/12
Project: Standard