KMT-2023-BLG-1866Lb: Microlensing super-Earth around an M dwarf host

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
e-mail: cheongho@astroph.chungbuk.ac.kr
² Institute of Natural and Mathematical Science, Massey University, Auckland 0745, New Zealand
³ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
⁴ Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
⁵ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁶ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁷ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
⁸ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
⁹ Center for Astrophysics | Harvard & Smithsonian 60 Garden St., Cambridge, MA 02138, USA
¹⁰ Department of Astronomy and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, PR China
¹¹ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea
¹² Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan
¹³ Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
¹⁴ Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁵ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
¹⁶ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁷ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁸ Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
¹⁹ Oak Ridge Associated Universities, Oak Ridge, TN 37830, USA
²⁰ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan
²¹ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
²² Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
²³ University of Canterbury Mt. John Observatory, PO Box 56, Lake Tekapo 8770, New Zealand
²⁴ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK

Received: 15 February 2024
Accepted: 10 May 2024

Abstract

Aims. We aim to investigate the nature of the short-term anomaly that appears in the lensing light curve of KMT-2023-BLG-1866. The anomaly was only partly covered due to its short duration of less than a day, coupled with cloudy weather conditions and a restricted nighttime duration.

Methods. Considering the intricacy of interpreting partially covered signals, we thoroughly explored all potential degenerate solutions. Through this process, we identified three planetary scenarios that account for the observed anomaly equally well. These scenarios are characterized by the specific planetary parameters: (s, q)_inner = [0.9740 ± 0.0083, (2.46 ± 1.07) × 10⁻⁵], (s, q)_intermediate = [0.9779 ± 0.0017, (1.56 ± 0.25) × 10⁻⁵], and (s, q)_outer = [0.9894 ± 0.0107, (2.31 ± 1.29) × 10⁻⁵], where s and q denote the projected separation (scaled to the Einstein radius) and mass ratio between the planet and its host, respectively. We identify that the ambiguity between the inner and outer solutions stems from the inner-outer degeneracy, while the similarity between the intermediate solution and the others is due to an accidental degeneracy caused by incomplete anomaly coverage.

Results. Through Bayesian analysis utilizing the constraints derived from measured lensing observables and blending flux, our estimation indicates that the lens system comprises a very-low-mass planet orbiting an early M-type star situated approximately (6.2–6.5) kpc from Earth in terms of median posterior values for the different solutions. The median mass of the planet host is in the range of (0.48–0.51) M_⊙, and that of the planet’s mass spans a range of (2.6–4.0) M_E, varying across different solutions. The detection of KMT-2023-BLG-1866Lb signifies the extension of the lensing surveys to very-low-mass planets that have been difficult to detect in earlier surveys.