OGLE-2012-BLG-0724Lb: a Saturn-mass planet around an M dwarf

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 $q=(1.58\pm 0.15)\times {10}^{-3}$. By conducting a Bayesian analysis, we estimate that the host star is an M dwarf with a mass of $M_L={0.29}_{-0.16}^{+0.33}{M}_{\odot }$ located at $D_L={6.7}_{-1.2}^{+1.1}kpc$ away from the Earth and the companion's mass is $m_P={0.47}_{-0.26}^{+0.54}{M}_{Jup}$. The projected planet–host separation is $a_{\perp }={1.6}_{-0.3}^{+0.4}AU$. 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 another example of a possible pileup of sub-Jupiters $(0.2<m_P/M_{Jup}<1)$ in contrast to a lack of Jupiters ($\sim 1\text{--}2M_{Jup}$) around M dwarfs, supporting the prediction by core accretion models that Jupiter-mass or more massive planets are unlikely to form around M dwarfs.