OGLE-2018-BLG-1185b: A Low-mass Microlensing Planet Orbiting a Low-mass Dwarf

Iona Kondo , Jennifer C. Yee , David P. Bennett , Takahiro Sumi , Naoki Koshimoto , Ian A. Bond , Andrew Gould , Andrzej Udalski , Yossi Shvartzvald , Youn Kil Jung , Weicheng Zang , Valerio Bozza , Etienne Bachelet , Markus P. G. Hundertmark , Nicholas J. Rattenbury , F. Abe , R. Barry , A. Bhattacharya , M. Donachie , A. Fukui , H. Fujii , Y. Hirao , S. Ishitani Silva , Y. Itow , R. Kirikawa , M. C. A. Li , Y. Matsubara , S. Miyazaki , Y. Muraki , G. Olmschenk , C. Ranc (1) , Y. Satoh , H. Shoji , D. Suzuki , Y. Tanaka , P. J. Tristram , T. Yamawaki , A. Yonehara , P. Mróz , R. Poleski , J. Skowron , M. K. Szymański , I. Soszyński , S. Kozłowski , P. Pietrukowicz , K. Ulaczyk , K. A. Rybicki , P. Iwanek , M. Wrona , M. D. Albrow , S. -J. Chung , C. Han , K. -H. Hwang , H. -W. Kim , I. -G. Shin , S. -M. Cha , D. -J. Kim , S. -L. Kim , C. -U. Lee , D. -J. Lee , Y. Lee , B. -G. Park , R. W. Pogge , Y. -H. Ryu , C. A. Beichman , G. Bryden , S. Calchi Novati , S. Carey , B. S. Gaudi , C. B. Henderson , W. Zhu , D. Maoz , M. T. Penny , M. Dominik , U. G. Jørgensen , P. Longa-Peña , N. Peixinho , S. Sajadian , J. Skottfelt , C. Snodgrass , J. Tregloan-Reed , M. J. Burgdorf , J. Campbell-White , S. Dib , Y. I. Fujii , T. C. Hinse , E. Khalouei , S. Rahvar , M. Rabus , J. Southworth , Y. Tsapras , R. A. Street , D. M. Bramich , A. Cassan (1) , K. Horne , J. Wambsganss , S. Mao , A. Saha

1 IAP - Institut d'Astrophysique de Paris

We report an analysis of the planetary microlensing event OGLE-2018-BLG-1185, which was observed by a large number of ground-based telescopes and by the Spitzer Space Telescope. The ground-based light curve indicates a low planet-host star mass ratio of q = (6.9 ± 0.2) × 10^-5, which is near the peak of the wide-orbit exoplanet mass-ratio distribution. We estimate the host star and planet masses with a Bayesian analysis using the measured angular Einstein radius under the assumption that stars of all masses have an equal probability of hosting the planet. The flux variation observed by Spitzer is marginal, but still places a constraint on the microlens parallax. Imposing a conservative constraint that this flux variation should be Δf_Spz < 4 instrumental flux units yields a host mass of ${M}_{\mathrm{host}}={0.37}_{-0.21}^{+0.35}\ {M}_{\odot }$ and a planet mass of ${m}_{{\rm{p}}}={8.4}_{-4.7}^{+7.9}\ {M}_{\oplus }$. A Bayesian analysis including the full parallax constraint from Spitzer suggests smaller host star and planet masses of ${M}_{\mathrm{host}}={0.091}_{-0.018}^{+0.064}\ {M}_{\odot }$ and ${m}_{{\rm{p}}}={2.1}_{-0.4}^{+1.5}\ {M}_{\oplus }$, respectively. Future high-resolution imaging observations with the Hubble Space Telescope or Extremely Large Telescope could distinguish between these two scenarios and help reveal the planetary system properties in more detail.

Keywords: Gravitational microlensing; Gravitational microlensing exoplanet detection; Satellite microlensing parallax; 672; 2147; 2148; Astrophysics - Earth and Planetary Astrophysics

Domains: Sciences of the Universe [physics]

Iona Kondo, Jennifer C. Yee, David P. Bennett, Takahiro Sumi, Naoki Koshimoto, et al.. OGLE-2018-BLG-1185b: A Low-mass Microlensing Planet Orbiting a Low-mass Dwarf. The Astronomical Journal, 2021, 162, ⟨10.3847/1538-3881/ac00ba⟩. ⟨insu-03748198⟩