Evolution of BD-14 3065b (TOI-4987b) from giant planet to brown dwarf as possible evidence of deuterium burning at old stellar ages^★

¹ Astronomical Institute, Czech Academy of Sciences, Fričova 298, 251 65, Ondřejov, Czech Republic
e-mail: johnysubjak@gmail.com
² Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
³ Facultad de Ingeniera y Ciencias, Universidad Adolfo Ibáñez, Av. Diagonal las Torres 2640, Peñalolén, Santiago, Chile
⁴ Millennium Institute for Astrophysics, Santiago, Chile
⁵ Data Observatory Foundation, Santiago, Chile
⁶ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁷ Thühringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁸ Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlarska 2, CZ-611 37, Brno, Czech Republic
⁹ Perth Exoplanet Survey Telescope (PEST), Perth, Western Australia, Australia
¹⁰ Department of Electrical Engineering and Centre of Astro-Engineering, Pontificia Universidad Catolica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
¹¹ Società Astronomica Lunae, Sarzana, Italy
¹² Department of Physics, Engineering and Astronomy, Stephen F. Austin State University, 1936 North St, Nacogdoches, TX 75962, USA
¹³ NASA Ames Research Center, Moffett Field, CA 94035, USA
¹⁴ Department of Physics and Astronomy, University of New Mexico, 210 Yale Blvd NE, Albuquerque, NM 87106, USA
¹⁵ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁶ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁷ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
¹⁸ SETI Institute, Mountain View, CA 94043 USA/NASA Ames Research Center, Moffett Field, CA 94035, USA
¹⁹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

Received: 19 December 2023
Accepted: 3 June 2024

Abstract

The present study confirms BD-14 3065b as a transiting planet-brown dwarf in a triple-star system, with a mass near the deuterium-burning boundary. BD-14 3065b has the largest radius observed within the sample of giant planets and brown dwarfs around post-main sequence stars. Its orbital period is 4.3 days and it transits a subgiant F-type star with a mass of M_* = 1.41 ± 0.05 M_⊙, a radius of R_* = 2.35 ± 0.08 R_⊙, an effective temperature of T_eff = 6935 ± 90 K, and a metallicity of −0.34 ± 0.05 dex. By combining TESS photometry with high-resolution spectra acquired with the TRES and Pucheros+ spectrographs, we measured a mass of M_⊙ = 12.37 ± 0.92 M_Jup and a radius of R_p = 1.926 ± 0.094 R_Jup. Our discussion of potential processes that could be responsible for the inflated radius led us to conclude that deuterium burning is a plausible explanation for the heating taking place in BD-14 3065b’s interior. Detections of the secondary eclipse with TESS photometry enabled a precise determination of the eccentricity, e_p = 0.066 ± 0.011, and reveal that BD-14 3065b has a brightness temperature of 3520 ± 130 K. With its unique characteristics, BD-14 3065b presents an excellent opportunity to study its atmosphere via thermal emission spectroscopy.