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

I. Kondo, J. C. Yee, D. Bennett, T. Sumi, N. Koshimoto, I. Bond, A. Gould, A. Udalski, Y. Shvartzvald, Y. K. Jung, W. Zang, V. Bozza, E. Bachelet, M. Hundertmark, N. Rattenbury, F. Abe, R. Barry, A. Bhattacharya, M. Donachie, A. Fukui, H. Fujii, Y. Hirao, S. I. Silva, Y. Itow, R. Kirikawa, M. C. A. Li, Y. Matsubara, S. Miyazaki, Y. Muraki, G. Olmschenk, C. Ranc, Y. Satoh, H. Shoji, D. Suzuki, Y. Tanaka, P. J. Tristram, T. Yamawaki, A. Yonehara, P. Mrůz, Radosaw Poleski, J. Skowron, M. K. Szymanski, I. Soszynski, S. Kozlowski, P. Pietrukowicz, K. Ulaczyk, K. A. Rybicki, P. Iwanek, M. Wrona, M. D. Albrow, S. -. Chung, C. Han, K. -. Hwang, H. -. Kim, I. -. Shin, S. -. Cha, D. -. Kim, S.-L. Kim, C. -. Lee, D. -. Lee, Y. Lee, B. -. Park, R. W. Pogge, Y. -. Ryu, C. Beichman, G. Bryden, S. Calchi Novati, S. Carey, B. S. Gaudi, Calen B. Henderson, W. Zhu, D. Maoz, Matthew Penny, M. Dominik, U. G. JÝrgensen, P. Longa-PeŮa, 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, K. Horne, J. Wambsganss, S. Mao, A. Saha, ROME/REA Project Team

Abstract
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 ΔfSpz < 4 instrumental flux units yields a host mass of Mhost=0.37+0.35−0.21 M and a planet mass of mp=8.4+7.9−4.7 M . A Bayesian analysis including the full parallax constraint from Spitzer suggests smaller host star and planet masses of Mhost=0.091+0.064−0.018 M and mp=2.1+1.5−0.4 M , 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

The Astronomical Journal
Volume 162(2, Number 77, Page 18
2021 August

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia