We report the discovery of an exoplanet from the analysis of the gravitational microlensing event OGLE-2015-BLG-1649 that challenges the core accretion model of planet formation and appears to support the disk instability model .
The planet/host-star mass ratio is q = 7.2 \times 10 ^ { -3 } and the projected separation normalized to the angular Einstein radius is s = 0.9 .
We conducted high-resolution follow-up observations using the IRCS camera on the Subaru telescope and are able to place an upper limit on the lens flux .
From these measurements we are able to exclude all host stars greater than or equal in mass to a G-type dwarf .
We conducted a Bayesian analysis with these new flux constraints included as priors resulting in estimates of the masses of the host star and planet .
These are M _ { L } = 0.34 \pm 0.19 ~ { } M _ { \odot } and M _ { p } = 2.5 ^ { +1.5 } _ { -1.4 } ~ { } M _ { Jup } , respectively .
The distance to the system is D _ { L } = 4.23 ^ { +1.51 } _ { -1.64 } ~ { } kpc .
The projected star-planet separation is a _ { \perp } = 2.07 ^ { +0.65 } _ { -0.77 } ~ { } AU .
The estimated relative lens-source proper motion , \sim 7.1 ~ { } { mas / yr } , is fairly high and thus the lens can be better constrained if additional follow-up observations are conducted several years after the event .