This work is based on data collected under the NGTS project at the European Southern Observatory (ESO) La Silla Paranal Observatory. The NGTS facility is operated by the consortium institutes with support from the UK Science and Technology Facilities Council (STFC) under projects ST/M001962/1, ST/S002642/1, and ST/W003163/1. This study is based on observations collected at the European Southern Observatory under ESO programme 105.20G9. This paper includes public data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. This paper uses observations made at the South African Astronomical Observatory (SAAO). This work has made use of data from the European Space Agency (ESA) mission Gaia (https: //www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web /gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular, the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the PanSTARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under grant no. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation grant no. AST1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. Some of the Observations in the paper made use of the highresolution Imaging instrument Zorro. Zorro was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Zorro was mounted on the Gemini South telescope of the international Gemini Observatory, a programme of NSF’s NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigacion´ y Desarrollo (Chile), Ministerio de Ciencia, Tecnolog´ıa e Innovacion´ (Argentina), Ministerio ´ da Ciencia, ˆ Tecnologia, Inovac¸oes ˜ e Comunicac¸oes ˜ (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). BH is supported by an STFC studentship (ST/S505511/1 and ST/T506242/1). SLC acknowledges support from an STFC Ernest Rutherford Fellowship (ST/R003726/1). The contribution of FB, ML, OT, and SU has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40 182901 and 51NF40 205606. ML acknowledges support of the Swiss National Science Foundation under grant number PCEFP2 194576. The contribution of EMB has been supported by STFCthrough the consolidated grant ST/W001136/1.CAC acknowledges that this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA (80NM0018D0004). JSJ gratefully acknowledges support by FONDECYT grant 1201371 and from the ANID BASAL projects ACE210002 and FB210003. The postdoctoral fellowship of KB is funded by FRS-FNRS grant T.0109.20 and by the Francqui Foundation. This publication benefits from the support of the French Community of Belgium in the context of the FRIA Doctoral grant awarded to MT. MG is FRS-FNRS Research Director and EJ is FRS–FNRS Senior Research Associate. FJP acknowledges financial support from the grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033 and through projects PID2019-109522GBC52 and PID2022-137241NB-C43. This research is in part funded by the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 803193/BEBOP), from the MERAC foundation, and from the Science and Technology Facilities Council (STFC; grant no. ST/S00193X/1 and ST/W000385/1). Based on data collected by the SPECULOOS-South Observatory at the ESO Paranal Observatory in Chile. The ULiege’s contribution to SPECULOOS has received funding from the European Research Councilunderthe European Union’s Seventh Framework Programme (FP/2007- 2013) (grant agreement no. 336480/SPECULOOS), from the Balzan Prize and Francqui Foundations, from the Belgian Scientific Research Foundation (FRS-FNRS; grant no. T.0109.20), from the University of Liege, and from the ARC grant for Concerted Research Actions financed by the Wallonia-Brussels Federation. This work is supported by a grant from the Simons Foundation (PI Queloz, grant number 327127). Based on data collected by the TRAPPIST-South telescope at the ESO La Silla Observatory. TRAPPIST is funded by the Belgian Fund for Scientific Research (Fond National de la Recherche Scientifique, FNRS) under the grant PDR T.0120.21, with the participation of the Swiss National Science Foundation (SNF).

Henderson, Beth A. et al.-- Full list of authors: Henderson, Beth A.; Casewell, Sarah L.; Goad, Michael R.; Acton, Jack S.; Günther, Maximilian N.; Nielsen, Louise D.; Burleigh, Matthew R.; Belardi, Claudia; Tilbrook, Rosanna H.; Turner, Oliver; Howell, Steve B.; Clark, Catherine A.; Littlefield, Colin; Barkaoui, Khalid; Alves, Douglas R.; Anderson, David R.; Bayliss, Daniel; Bouchy, Francois; Bryant, Edward M.; Dransfield, George; Ducrot, Elsa; Eigmüller, Philipp; Gill, Samuel; Gillen, Edward; Gillon, Michaël; Hawthorn, Faith; Hooton, Matthew J.; Jackman, James A. G.; Jehin, Emmanuel; Jenkins, James S.; Kendall, Alicia; Lendl, Monika; McCormac, James; Moyano, Maximiliano; Pedersen, Peter Pihlmann; Pozuelos, Francisco J.; Ramsay, Gavin; Sefako, Ramotholo R.; Timmermans, Mathilde; Triaud, Amaury H. M. J.; Udry, Stephane; Vines, Jose I.; Watson, Christopher A.; West, Richard G.; Wheatley, Peter J.; Zúñiga-Fernández, Sebastián.-- This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

We report the disco v ery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Surv e y data, with supporting observations found in TESS sectors 11 and 38. We confirmed the disco v ery with follow- up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterize the system. We find an orbital period of ∼1.25 d, a mass of 69 . 0 + 5 . 3 -4 . 8 M J , close to the hydrogen burning limit, and a radius of 0.95 ±0.05 R J . We determine the age to be > 0.5 Gyr, using model isochrones, which is found to be in agreement with spectral energy distribution fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important disco v ery within this scarcely populated region. © 2024 The Author(s)

With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).

Peer reviewed