AT2021uey: A planetary microlensing event outside the Galactic bulge

¹ University of Warsaw, Astronomical Observatory, Warszawa, Poland
² Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
³ Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France
⁴ Institute of Theoretical Physics and Astronomy, Vilnius University, Vilnius, Lithuania
⁵ Institut d’Astrophysique de Paris (IAP), Sorbonne Université, CNRS, Paris, France
⁶ IPAC, Mail Code 100-22, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁷ Dipartimento di Fisica “E.R. Caianiello”, Università di Salerno, Fisciano, Italy
⁸ Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli, Italy
⁹ Flarestar Observatory, San Gwann, Malta
¹⁰ INAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Bologna, Italy
¹¹ School of Physics, Trinity College Dublin, Dublin, Ireland
¹² Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), Martì i Franquès 1, 08028 Barcelona, Spain
¹³ University of St Andrews, Centre for Exoplanet Science, SUPA School of Physics & Astronomy, UK
¹⁴ Public observatory Astrolab IRIS, Zillebeke, Belgium
¹⁵ Millennium Institute of Astrophysics MAS, Nuncio Monsenor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile
¹⁶ Komaba Institute for Science, The University of Tokyo, Tokyo, Japan
¹⁷ Instituto de Astrofísica de Canarias (IAC), Tenerife, Spain
¹⁸ Institute of Earth System, University of Malta, Malta
¹⁹ Znith Astronomy Observatory, Malta
²⁰ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Heidelberg, Germany
²¹ Evgeni Kharadze Georgian National Astrophysical Observatory, Abastumani, Georgia
²² Astronomical Institute, University of Wrocław, ul. M. Kopernika 11, 51-622, Wrocław, Poland
²³ Astrobiology Center, Tokyo, Japan
²⁴ Horten videregående skole Horten, Norway
²⁵ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot, Israel
²⁶ Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Goleta, CA 93117, USA
²⁷ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Toruń, Toruń, Poland
²⁸ Institut d’Estudis Espacials de Catalunya (IEEC), Esteve Terradas, 1, Edifici RDIT, Campus PMT-UPC, 08860 Castelldefels (Barcelona), Spain
²⁹ National Centre for Nuclear Research, Pasteura 7, 02-093 Warsaw, Poland
³⁰ Janusz Gil Institute of Astronomy, University of Zielona Gora, Lubuska 2, 65-265 Zielona Gora, Poland
³¹ Astronomical Observatory, Jagiellonian University, Orla 171, 30-244 Kraków, Poland
³² Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³³ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
³⁴ Departament de Física Quàntica i Astrofìsica (FQA), Universitat de Barcelona (UB), Martì i Franquès 1, 08028 Barcelona, Spain
³⁵ Independent researcher, Warszawa, Poland

^★ Corresponding author: m_ban@hotmail.co.uk

Received: 23 February 2025
Accepted: 26 March 2025

Abstract

We report the analysis of a planetary microlensing event AT2021uey. The event was observed outside the Galactic bulge and alerted both space-(Gaia) and ground-based (ZTF and ASAS-SN) surveys. From the observed data, we find that the lens system is located at a distance of ∼1 kpc and comprises an M-dwarf host star of about half a solar mass, orbited by a Jupiter-like planet beyond the snowline. The source star could be a metal-poor giant located in the halo according to the spectral analyses and modelling. Hence, AT2021uey is a unique example of the binary-lens event outside the bulge that is offered by a disc-halo lens-source combination.