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. Mróz, 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. -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. Beichman, G. Bryden, S. Calchi Novati, S. Carey, B. S. Gaudi, Calen B. Henderson, W. Zhu, D. Maoz, Matthew 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, 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 Δf_Spz < 4 instrumental flux units yields a host mass of M_host=0.37^+0.35_−0.21 M_⊙ and a planet mass of m_p=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 M_host=0.091^+0.064_−0.018 M_⊙ and m_p=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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