BD-14 3065b (TOI-4987b): from giant planet to brown dwarf: evidence for deuterium burning in old age?

Abstract

The present study reports the confirmation of BD-14 3065b, 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 $M_{\star }=1.41\pm 0.05M_{\odot }$, a radius of $R_{\star }=2.35\pm 0.08R_{\odot }$, an effective temperature of $T_{\mathrm{eff}}=6935\pm 90$ K, and a metallicity of $-0.34\pm 0.05$ dex. By combining TESS photometry with high-resolution spectra acquired with the TRES and Pucheros+ spectrographs, we measured a mass of $M_p=12.37\pm 0.92M_J$ and a radius of $R_p=1.926\pm 0.094R_J$. Our discussion of potential processes that could be responsible for the inflated radius led us to conclude that deuterium burning is a plausible explanation resulting from the heating of BD-14 3065b's interior. Detection of the secondary eclipse with TESS photometry enables a precise determination of the eccentricity $e_p=0.066\pm 0.011$ and reveals BD-14 3065b has a brightness temperature of $3520\pm 130$ K. With its unique characteristics, BD-14 3065b presents an excellent opportunity to study its atmosphere through thermal emission spectroscopy.

23 pages, 22 figures, accepted for publication in Astronomy & Astrophysics