OGLE-2018-BLG-1269Lb: A Jovian Planet with a Bright I = 16 Host

We report the discovery of a planet in the microlensing event OGLE-2018-BLG-1269 with a planet-host mass ratio q ˜ 6 × 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 $({M}{2}={0.69}{-0.22}^{+0.44},{M}{{\rm{J}}})$ orbiting a Sun-like star $({M}{1}={1.13}{-0.35}^{+0.72},{M}{\odot })$ at a distance of ${D}{{\rm{L}}}={2.56}{-0.62}^{+0.92},\mathrm{kpc}$ . The projected planet-host separation is ${a}{\perp }={4.61}{-1.17}^{+1.70},\mathrm{au}$ . Using Gaia astrometry, we show that the blended light lies $\lesssim 12,\mathrm{mas}$ 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 $0.0\leqslant [\mathrm{Fe}/{\rm{H}}]\leqslant +0.3$ , the host and planet masses are then in the range of $1.16\leqslant {M}{1}/{M}{\odot }\leqslant 1.38$ and $0.74\leqslant {M}{2}/{M}{{\rm{J}}}\leqslant 0.89$ , respectively. Low host metallicities are excluded. The brightness and proximity of the lens make the event a strong candidate for spectroscopic follow-up both to test the microlensing solution and to further characterize the system.