Spitzer as Microlens Parallax Satellite: Mass Measurement for the OGLE-2014-BLG-0124L Planet and its Host Star

Abstract

We combine Spitzer and ground-based observations to measure the microlens parallax vector ${\mathbf \pi}_{\rm E}$, and so the mass and distance of OGLE-2014-BLG-0124L, making it the first microlensing planetary system with a space-based parallax measurement. The planet and star have masses $m \sim 0.5\,M_{\rm jup}$ and $M\sim 0.7\,M_\odot$ and are separated by $a_\perp\sim 3.1$ AU in projection. The main source of uncertainty in all these numbers (approximately 30%, 30%, and 20%) is the relatively poor measurement of the Einstein radius $\theta_{\rm E}$, rather than uncertainty in $\pi_{\rm E}$, which is measured with 2.5% precision. This compares to 22% based on OGLE data alone, implying that the Spitzer data provide not only a substantial improvement in the precision of the $\pi_{\rm E}$ measurement but also the first independent test of a ground-based ${\mathbf \pi}_{\rm E}$ measurement.