OGLE-2015-BLG-1609Lb: A sub-Jovian planet orbiting a low-mass stellar or brown dwarf host

¹ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
² Department of Earth and Space Science, Graduate School of Science, Osaka University,Toyonaka, Osaka 560-0043, Japan
³ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12–14, 69120 Heidelberg, Germany
⁴ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
⁵ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁶ Villanova University, Department of Astrophysics and Planetary Sciences, 800 Lancaster Ave., Villanova, PA 19085, USA
⁷ Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan
⁸ Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁹ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
¹⁰ Institute of Natural and Mathematical Sciences, Massey University, Auckland 0745, New Zealand
¹¹ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹² Instituto de Astrofísica de Canarias, Vía Lacteá s/n, 38205 La Laguna, Tenerife, Spain
¹³ Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
¹⁴ Oak Ridge Associated Universities, Oak Ridge, TN 37830, USA
¹⁵ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Kanagawa 252-5210, Japan
¹⁶ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
¹⁷ Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
¹⁸ University of Canterbury Mt. John Observatory, P.O. Box 56, Lake Tekapo 8770, New Zealand
¹⁹ Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, suite 102, Goleta, CA 93117, USA
²⁰ IPAC, Mail Code 100-22, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA
²¹ Università degli Studi di Salerno, Dipartimento di Fisica “E.R. Caianiello”, via Ponte Don Melillo, 84085 Fisciano (SA), Italy
²² Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Via Cintia, Napoli 80126, Italy
²³ SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
²⁴ Millennium Institute of Astrophysics MAS, Nuncio Monsenor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile
²⁵ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
²⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
²⁷ Astrophysics Research Institute, Liverpool John Moores University, Liverpool CH41 1LD, UK
²⁸ South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
²⁹ Centre for ExoLife Sciences, Niels Bohr Institute, University of Copenhagen, Jagtvej 155, 2200 Copenhagen, Denmark
³⁰ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Avda. U. de Antofagasta 02800, Antofagasta, Chile
³¹ Instituto de Astrofísica e Ciências do Espaço, Universidade de Coimbra, 3040-004 Coimbra, Portugal
³² Centre for Electronic Imaging, Department of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
³³ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
³⁴ Universität Hamburg, Faculty of Mathematics, Informatics and Natural Sciences, Department of Earth Sciences, Meteorological Institute, Bundesstraße 55, 20146 Hamburg, Germany
³⁵ Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Macul 7820436, Santiago, Chile
³⁶ University of Southern Denmark, Department of Physics, Chemistry and Pharmacy, SDU-Galaxy, Campusvej 55, 5230 Odense M, Denmark
³⁷ Jodrell Bank, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
³⁸ Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy
³⁹ Max Planck Institute for Astronomy, Königstuhl 17, 69117, Heidelberg, Germany
⁴⁰ INAF – Turin Astrophysical Observatory, Via Osservatorio 20, I-10025, Pino Torinese, Italy
⁴¹ Universidad Catolica de la Santisima, Concepcion, Chile
⁴² Department of Physics, Sharif University of Technology, PO Box 11155-9161, Tehran, Iran

^★ Corresponding author.

Received: 16 December 2024
Accepted: 2 April 2025

Abstract

We present a comprehensive analysis of the planetary microlensing event OGLE-2015-BLG-1609. The planetary anomaly was detected by two survey telescopes, OGLE and MOA. Both surveys collected enough data over the planetary anomaly to enable an unambiguous planet detection. Such survey detections of planetary anomalies are needed to build a robust sample of planets, which could improve studies on the microlensing planetary occurrence rate by reducing biases and statistical uncertainties. In this work we examined different methods for modeling microlensing events using individual datasets. In particular, we incorporated a Galactic model prior to better constrain the poorly defined microlensing parallax. Ultimately, we fitted a comprehensive model to all available data, identifying three potential topologies, with two showing comparably high Bayesian evidence. Our analysis indicates that the host of the planet is either a brown dwarf, with a probability of 34%, or a low-mass stellar object (M dwarf), with a probability of 66%. The topology that provides the best fit to the data results in an extraordinary low host mass, M_h = 0.025^+0.050_-0.012M_⊙, accompanied by an Earth-mass planet with M_c = 1.9^+3.9_-1.0M_⊕.