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. FukuiH. Fujii, Y. Hirao, S. Ishitani 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, 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, K. Horne, J. Wambsganss, S. Mao, A. Saha

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We report the analysis of 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 lightcurve indicates a low planet-host star mass ratio of q = (6.9 ± 0.2) x 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 to host this planet. The flux variation observed by Spitzer was 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 indicates 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 HST or ELTs could distinguish between these two scenarios and help to reveal the planetary system properties in more detail.
Original languageEnglish
Article number77
Number of pages18
JournalAstronomical Journal
Issue number2
Early online date29 Jul 2021
Publication statusPublished - 1 Aug 2021


  • Gravitational microlensing
  • Gravitational microlensing exoplanet detection
  • Satellite microlensing parallax


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