Precise mass measurement of OGLE-2013-BLG-0132/MOA-2013-BLG-148: a Saturn mass planet orbiting an M-dwarf

Abstract

We revisit the planetary microlensing event OGLE-2013-BLG-0132/MOA-2013-BLG-148 using Keck adaptive optics imaging in 2013 with NIRC2 and in 2020, 7.4 years after the event, with OSIRIS. The 2020 observations yield a source and lens separation of $56.91\pm 0.29$ mas, which provides us with a precise measurement of the heliocentric proper motion of the event $\hat{I}{¼}_{rel,hel}=7.695\pm 0.039$ mas $y{r}^{-1}$. We measured the magnitude of the lens in K-band as $K_{lens}=18.69\pm 0.04$. Using these constraints, we refit the microlensing light curve and undertake a full reanalysis of the event parameters including the microlensing parallax $\ddot{I}{€}_E$ and the distance to the source D${}_S$. We confirm the results obtained in the initial study by \cite{Mroz_2017} and improve significantly upon the accuracy of the physical parameters. The system is an M dwarf of $0.495\pm 0.054$ $M_{\odot }$ orbited by a cold, Saturn-mass planet of $0.26\pm 0.028$ $M_{Jup}$ at projected separation $r_{\perp }$ = 3.14 $\pm$ 0.28 AU. This work confirms that the planetary system is at a distance of 3.48 $\pm$ 0.36 kpc, which places it in the Galactic disk and not the Galactic bulge.

16 pages, 7 figures. Resubmitted to AJ after minor revisions