$Spitzer$ Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M-dwarf
Creators: name: Jung, Youn Kil
name: Gould, Andrew
name: Udalski, Andrzej
name: Sumi, Takahiro
name: Yee, Jennifer C.
name: Shvartzvald, Yossi
name: Zang, Weicheng
name: Han, Cheongho
name: Albrow, Michael D.
name: Chung, Sun Ju
name: Hwang, Kyu-Ha
name: Ryu, Yoon-Hyun
name: Shin, In-Gu
name: Zhu, Wei
name: Cha, Sang-Mok
name: Kim, Dong-Jin
name: Kim, Hyoun-Woo
name: Kim, Seung-Lee
name: Lee, Chung-Uk
name: Lee, Dong-Joo
name: Lee, Yongseok
name: Park, Byeong-Gon
name: Pogge, Richard W.
name: Mróz, Przemek
name: Szymański, Michał K.
name: Skowron, Jan
name: Poleski, Radek
name: Soszyński, Igor
name: Pietrukowicz, Paweł
name: Kozłowski, Szymon
name: Ulaczyk, Krzystof
name: Rybicki, Krzysztof A.
name: Iwanek, Patryk
name: Wrona, Marcin
name: Beichman, Charles A.
name: Bryden, Geoffery
name: Novati, Sebastiano Calchi
name: Carey, Sean
name: Gaudi, B. Scott
name: Henderson, Calen B.
name: Abe, Fumio
name: Barry, Richard
name: Bennett, David P.
name: Bond, Ian A.
name: Bhattacharya, Aparna
name: Donachie, Martin
name: Fukui, Akihiko
name: Hirao, Yuki
name: Itow, Yoshitaka
name: Kondo, Iona
name: Koshimoto, Naoki
name: Li, Man Cheung Alex
name: Matsubara, Yutaka
name: Miyazaki, Shota
name: Muraki, Yasushi
name: Nagakane, Masayuki
name: Ranc, Clément
name: Rattenbury, Nicholas J.
name: Suematsu, Haruno
name: Sullivan, Denis J.
name: Suzuki, Daisuke
name: Tristram, Paul J.
name: Yonehara, Atsunori
name: Jacklin, Savannah
name: Penny, Matthew T.
name: Stassun, Keivan G.
Publisher: name: arXiv
Year: 2019
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We report the discovery of a $Spitzer$ microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio $q \sim 2\times10^{-4}$. The planetary signal, which is characterized by a short $(\sim 1~{\rm day})$ "bump" on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a "Hollywood" geometry. Combined with the source proper motion measured from $Gaia$, the $Spitzer$ satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of $M_{\rm p} = 13.9\pm1.6~M_{\oplus}$ orbiting a mid M-dwarf with a mass of $M_{\rm h} = 0.23\pm0.03~M_{\odot}$. There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields $M_{\rm p} = 1.2\pm0.2~M_{\oplus}$ and $M_{\rm h} = 0.15\pm0.02~M_{\odot}$. By combining the microlensing and $Gaia$ data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance $D_{\rm L} \sim 6\pm1~{\rm kpc}$. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy.
description: 34 pages, 8 figures, Submitted to AAS journal