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 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 orbiting a Sun-like star at a distance of . The projected planet–host separation is . Using Gaia astrometry, we show that the blended light lies 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 , the host and planet masses are then in the range of and , 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.