标题： OGLE-2012-BLG-0724Lb: 一颗土星质量的行星围绕M型矮星 显示英文标题

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

摘要： 我们报告了通过微引力透镜法发现的一颗行星 OGLE-2012-BLG-0724Lb。 尽管此事件的行星信号持续时间是已知最短的行星事件之一，但由于巡天小组 OGLE 和 MOA 进行了高频率观测，这一异常现象得到了很好的覆盖。 通过对光变曲线的分析，发现该行星系统的质量比为$q=(1.58\pm0.15)\times10^{-3}$。 通过贝叶斯分析，我们估计宿主恒星是一颗位于距离地球$D_{\rm L}=6.7_{-1.2}^{+1.1} \ {\rm kpc}$处、质量为$M_{\rm L}=0.29_{-0.16}^{+0.33} \ M_{\odot}$的 M 型矮星，伴星的质量为$m_{\rm P}=0.47_{-0.26}^{+0.54} \ M_{\rm Jup}$。 投影的行星与宿主恒星之间的分离距离为$a_{\perp}=1.6_{-0.3}^{+0.4} \ {\rm AU}$。 由于透镜源相对自行速度较高，未来高分辨率图像将能够探测到透镜宿主恒星，并唯一确定透镜的性质。 这个系统很可能是一颗围绕 M 型矮星的土星质量系外行星，这类系统常通过引力微透镜法被探测到。 这为可能存在的 M 型矮星周围子木星（$(0.2 < m_{\rm P}/M_{\rm Jup} < 1)$）的聚集提供了一个例子，与缺乏木星（$\sim 1 - 2 \ M_{\rm Jup}$）的情况形成对比，支持了核心吸积模型的预测，即木星质量或更高质量的行星不太可能在 M 型矮星周围形成。 显示英文摘要

摘要： 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 $q=(1.58\pm0.15)\times10^{-3}$. By conducting a Bayesian analysis, we estimate that the host star is an M-dwarf star with a mass of $M_{\rm L}=0.29_{-0.16}^{+0.33} \ M_{\odot}$ located at $D_{\rm L}=6.7_{-1.2}^{+1.1} \ {\rm kpc}$ away from the Earth and the companion's mass is $m_{\rm P}=0.47_{-0.26}^{+0.54} \ M_{\rm Jup}$. The projected planet-host separation is $a_{\perp}=1.6_{-0.3}^{+0.4} \ {\rm AU}$. 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 $(0.2 < m_{\rm P}/M_{\rm Jup} < 1)$ in contrast to a lack of Jupiters ($\sim 1 - 2 \ M_{\rm Jup}$) around M-dwarfs, supporting the prediction by core accretion models that Jupiter-mass or more massive planets are unlikely to form around M-dwarfs.