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 _ { J } ) orbiting a Sun-like star ( M _ { 1 } = 1.13 _ { -0.35 } ^ { +0.72 } M _ { \odot } ) at a distance of D _ { L } = 2.56 _ { -0.62 } ^ { +0.92 } { kpc } .
The projected planet-host separation is a _ { \perp } = 4.61 _ { -1.17 } ^ { +1.70 } { au } .
Using 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 \leq { [ Fe / H ] } \leq + 0.3 , the host and planet masses are then in the range of 1.16 \leq M _ { 1 } / M _ { \odot } \leq 1.38 and 0.74 \leq M _ { 2 } / M _ { J } \leq 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 .