OGLE-2017-BLG-0406: Spitzer Microlens Parallax Reveals Saturn-mass Planet Orbiting M-dwarf Host in the Inner Galactic Disk

Hirao, Yuki; Bennett, David P.; Ryu, Yoon-Hyun; Koshimoto, Naoki; Udalski, Andrzej; Yee, Jennifer C.; Sumi, Takahiro; Bond, Ian A.; Shvartzvald, Yossi; Abe, Fumio et al.
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The Astronomical Journal

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We report the discovery and analysis of the planetary microlensing event OGLE-2017-BLG-0406, which was observed both from the ground and by the Spitzer satellite in a solar orbit. At high magnification, the anomaly in the light curve was densely observed by ground-based-survey and follow-up groups, and it was found to be explained by a planetary lens with a planet/host mass ratio of $q=7.0\times {10}^{-4}$?--> <!-- --> from the light-curve modeling. The ground-only and Spitzer-"only" data each provide very strong one-dimensional (1D) constraints on the 2D microlens parallax vector ${{\boldsymbol{\pi }}}_{{\rm{E}}}$?--> <!-- --> . When combined, these yield a precise measurement of ${{\boldsymbol{\pi }}}_{{\rm{E}}}$?--> <!-- --> and of the masses of the host ${M}_{\mathrm{host}}=0.56\pm 0.07\,{M}_{\odot }$?--> <!-- --> and planet Mplanet = 0.41 ± 0.05 MJup. The system lies at a distance DL = 5.2 ± 0.5 kpc from the Sun toward the Galactic bulge, and the host is more likely to be a disk population star according to the kinematics of the lens. The projected separation of the planet from the host is ${a}_{\perp }=3.5\pm 0.3\,\mathrm{au}$?--> <!-- --> (i.e., just over twice the snow line). The Galactic-disk kinematics are established in part from a precise measurement of the source proper motion based on OGLE-IV data. By contrast, the Gaia proper-motion measurement of the source suffers from a catastrophic 10σ error.