OGLE-2018-BLG-1269Lb: A Jovian Planet With A Bright, $I=16$ Host

Abstract

We report the discovery of a planet in the microlensing event OGLE-2018-BLG-1269, with planet-host mass ratio $q\sim 6\times 10^{-4}$, i.e., $0.6$ times smaller than the Jupiter/Sun mass ratio. Combined with the $Gaia$ parallax and proper motion, a strong one-dimensional constraint on the microlens parallax vector allows us to significantly reduce the uncertainties of lens physical parameters. A Bayesian analysis that ignores any information about light from the host yields that the planet is a cold giant $(M_2=0.69_{-0.22}^{+0.44}{M}_{\mathrm{J}})$ orbiting a Sun-like star $(M_1=1.13_{-0.35}^{+0.72}{M}_{\odot })$ at a distance of $D_{\mathrm{L}}=2.56_{-0.62}^{+0.92}\mathrm{kpc}$. The projected planet-host separation is $a_{\perp }=4.61_{-1.17}^{+1.70}\mathrm{au}$. Using {\it Gaia} astrometry, we show that the blended light lies $\lesssim 12$mas from the host and therefore must be either the host star or a stellar companion to the host. An isochrone analysis favors the former possibility at $>99.6\%$. The host is therefore a subgiant. For host metallicities in the range of $0.0\le [Fe/H]\le +0.3$, the host and planet masses are then in the range of $1.16\le M_1/M_{\odot }\le 1.38$ and $0.74\le M_2/M_{\mathrm{J}}\le 0.89$, respectively. Low host metallicities are excluded. The brightness and proximity of the lens make the event a strong candidate for spectroscopic followup both to test the microlensing solution and to further characterize the system.

40 pages, 11 figures, and 3 tables