Wednesday, July 27, 2016

OGLE-2012-BLG-0724Lb: a Saturn Class Gas Giant Orbitng a M Dwarf Star

OGLE-2012-BLG-0724Lb: A Saturn-mass Planet around an M-dwarf


Hirao et al


We report the discovery of a planet by the microlensing method, OGLE-2012-BLG-0724Lb. Although the duration of the planetary signal for this event was one of the shortest seen for a planetary event, the anomaly was well covered thanks to high cadence observations taken by the survey groups OGLE and MOA. By analyzing the light curve, this planetary system is found to have a mass ratio q=(1.58±0.15)×10−3. By conducting a Bayesian analysis, we estimate that the host star is an M-dwarf star with a mass of ML=0.29+0.33−0.16 M⊙ located at DL=6.7+1.1−1.2 kpc away from the Earth and the companion's mass is mP=0.47+0.54−0.26 MJup. The projected planet-host separation is a⊥=1.6+0.4−0.3 AU. Because the lens-source relative proper motion is relatively high, future high resolution images would detect the lens host star and determine the lens properties uniquely. This system is likely a Saturn-mass exoplanet around an M-dwarf and such systems are commonly detected by gravitational microlensing. This adds an another example of a possible pileup of sub-Jupiters (0.2 less than mP/MJup less than 1) in contrast to a lack of Jupiters (∼1−2 MJup) around M-dwarfs, supporting the prediction by core accretion models that Jupiter-mass or more massive planets are unlikely to form around M-dwarfs.

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