TOI-503: The First Known Brown-dwarf Am-star Binary from the TESS Mission*

Abstract

We report the discovery of an intermediate-mass transiting brown dwarf (BD), TOI-503b, from the TESS mission. TOI-503b is the first BD discovered by TESS, and it has circular orbit around a metallic-line A-type star with a period of P = 3.6772 ± 0.0001 days. The light curve from TESS indicates that TOI-503b transits its host star in a grazing manner, which limits the precision with which we measure the BD’s radius ( ). We obtained high-resolution spectroscopic observations with the FIES, Ondřejov, PARAS, Tautenburg, and TRES spectrographs, and measured the mass of TOI-503b to be M b = 53.7 ± 1.2 . The host star has a mass of M ⋆ = 1.80 ± 0.06 M ⊙, a radius of R ⋆ = 1.70 ± 0.05R ⊙, an effective temperature of T eff = 7650 ± 160 K, and a relatively high metallicity of 0.61 ± 0.07 dex. We used stellar isochrones to derive the age of the system to be ∼180 Myr, which places its age between that of RIK 72b (a ∼10 Myr old BD in the Upper Scorpius stellar association) and AD 3116b (a ∼600 Myr old BD in the Praesepe cluster). Given the difficulty in measuring the tidal interactions between BDs and their host stars, we cannot precisely say whether this BD formed in situ or has had its orbit circularized by its host star over the relatively short age of the system. Instead, we offer an examination of plausible values for the tidal quality factor for the star and BD. TOI-503b joins a growing number of known short-period, intermediate-mass BDs orbiting main-sequence stars, and is the second such BD known to transit an A star, after HATS-70b. With the growth in the population in this regime, the driest region in the BD desert ( ) is reforesting.

Two Intermediate-mass Transiting Brown Dwarfs from the TESS Mission

“…Including the 2 new BDs in this work, the total number of known BDs that transit a star is 23 ( Table 7). With the discovery of TOI-569b and TOI-1406b, the total number of new transiting BDs discovered or observed by the TESS mission is now 4 (Jackman et al 2019;Subjak et al 2020;this work). We expect at least as many more to be discovered as TESS continues its observations over the remainder of its primary mission.…”

“…This is where the Transiting Exoplanet Survey Satellite (TESS) mission plays a major role. The transit method has been most successful in the characterization of BDs in relatively short orbital periods (on the order of 10-20 days or less to detect multiple transits), which is why the TESS mission has been particularly useful in making the initial detections of recently discovered transiting BDs (e.g., Jackman et al 2019;Subjak et al 2020). The transit light curves from TESS are taken over roughly 28 consecutive days per sector (or up to 1 year for overlapping sectors), with occasional gaps in coverage due to data downloads and instrumental anomalies.…”

TOI-2119: A transiting brown dwarf orbiting an active M-dwarf from NASA's TESS mission

“…We are now poised to more thoroughly explore this question of formation mechanism by examining the emerging transiting BD population with the Transiting Exoplanet Survey Satellite (TESS) mission (Ricker et al 2015). Transiting BDs are key as they enable us to measure the BD's mass and radius, which typically ranges from 0.7 − 1.4 Jupiter radii ( R J ) around main sequence host stars (Deleuil et al 2008;Subjak et al 2020;Carmichael et al 2020). Though transit detections typically restrict us to exploring a parameter space for short-period BDs (usually 𝑃 orb < 30 days to efficiently detect and characterise multiple transits), they play a critical role in filling out the population of BDs with measured masses and surface gravity (log 𝑔) estimates.…”

“…After delivering several new transiting BD discoveries during its two-year primary mission (e.g. Jackman et al 2019;Subjak et al 2020;Benni et al 2020;Carmichael et al 2020Carmichael et al , 2021, TESS continues to serve as our primary detection tool for new transiting BDs in its extended missions (e.g. Artigau et al 2021;Grieves et al 2021).…”

Discovery of a young low-mass brown dwarf transiting a fast-rotating F-type star by the Galactic Plane eXoplanet (GPX) survey

“…Current statistics of the observed properties of BDs indicates that two distinct populations exist: massive BDs ( 40 Jup ), which are formed similar to binary stars, and low-mass BDs, which are formed as planets (e.g., Ma & Ge 2014;Wilson et al 2016). However, this division of BDs into two populations is being challenged with the new discoveries of intermediate-mass BDs (Carmichael et al 2019(Carmichael et al , 2020Jackman et al 2019;Šubjak et al 2020).…”