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

TL;DR

This paper presents the first mass measurement of a microlensing planet using only microlens parallax and lens flux, demonstrating a new method applicable when finite source effects are undetectable.

Contribution

The study introduces a novel technique combining microlens parallax and lens flux measurements to determine planet and host star masses without finite source effects.

Findings

First mass measurement from microlens parallax and lens flux alone.

Demonstrates method's potential for future space-based microlensing surveys.

Identifies a planet with 35 Earth masses orbiting an M-dwarf at 3 kpc.

Abstract

We report the discovery of a microlensing planet OGLE-2012-BLG-0950Lb with the planet/host mass ratio of $q \sim 2 \times 10^{-4}$. 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 $M_{\rm p} = 35^{+17}_{-9} M_{\oplus}$ is orbiting around a M-dwarf with mass of $M_{\rm host} = 0.56^{+0.12}_{-0.16} M_{\odot}$ with a planet-host projected separation of $r_{\perp} =2.7^{+0.6}_{-0.7}$ AU located at $D_{\rm L} = 3.0^{+0.8}_{-1.1}$ kpc from us. This is the first mass measurement from only microlens parallax and the lens flux without the finite source effect. 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.