OGLE-2012-BLG-0950Lb: a 2 Neptune Mass M Dwarf World

OGLE-2012-BLG-0950Lb: The Possible First Planet Mass Measurement from Only Microlens Parallax and Lens Flux

Authors:

Koshimoto et al

Abstract:

We report the discovery of a microlensing planet OGLE-2012-BLG-0950Lb with the planet/host mass ratio of q=2×10−4. A long term distortion detected in both MOA and OGLE light curve can be explained by the microlens parallax due to the Earth's orbital motion around the Sun. Although the finite source effect is not detected, we obtain the lens flux by the high resolution Keck AO observation. Combining the microlens parallax and the lens flux reveal the nature of the lens: a planet with mass of Mp=35+17−9MEarth is orbiting around a M-dwarf with mass of Mh=0.56+0.12−0.16MSun with a planet-host projected separation of rproj=2.7+0.6−0.7 AU located at DL=3.0+0.8−1.1 kpc from us. This is the first mass measurement from only microlens parallax and the lens flux without the finite source effect. The long term distortion can also be explained by the source orbital motion (xallarap) which is suspicious but not ruled out. These models can be distinguished by future high resolution imaging because of the much larger lens-source relative proper motion and brighter lens in the parallax model compared to the xallarap model. In the coming space observation-era with Spitzer, K2, Euclid, and WFIRST, we expect many such events for which we will not be able to measure any finite source effect. This work demonstrates an ability of mass measurements in such events.