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Greening of the brown-dwarf desert EPIC 212036875b: a 51 M-J object in a 5-day orbit around an F7V star

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PERSSON Carina M. CSIZMADIA Szilard MUSTILL Alexander J. FRIDLUND Malcolm HATZES Artie P. NOWAK Grzegorz GEORGIEVA Iskra GANDOLFI Davide DAVIES Melvyn B. LIVINGSTON John H. PALLE Enric RODRIGUEZ Pilar ENDL Michael HIRANO Teruyuki PRIETO-ARRANZ Jorge KORTH Judith GRZIWA Sascha ESPOSITO Massimiliano ALBRECHT Simon JOHNSON Marshall C. BARRAGAN Oscar PARVIAINEN Hannu VAN Eylen Vincent SOBRINO Roi BECK Paul G. CABRERA Juan CARLEO Ilaria COCHRAN William D. DAI Fei DEEG Hans J. DE LEON Jerome P. EIGMULLER Philipp ERIKSON Anders FUKUI Akai GONZALEZ-CUESTA Lucia GUENTHER Eike W. HIDALGO Diego HJORTH Maria KABÁTH Petr KNUDSTRUP Emil KUSAKABE Nobuhiko LAM Kristine W. F. LUND Mikkel N. LUQUE Rafael MATHUR Savita MURGAS Felipe NARITA Norio NESPRAL David NIRAULA Prajwal OLOFSSON A. O. Henrik PATZOLD Martin RAUER Heike REDFIELD Seth RIBAS Ignasi SKARKA Marek SMITH Alexis M. S. SUBJAK Jan TAMURA Motohide

Rok publikování 2019
Druh Článek v odborném periodiku
Časopis / Zdroj ASTRONOMY & ASTROPHYSICS
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Citace
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Doi http://dx.doi.org/10.1051/0004-6361/201935505
Klíčová slova planetary systems; stars: fundamental parameters; stars: individual: EPIC 212036875; techniques: photometric; techniques: radial velocities
Popis Context. Although more than 2000 brown dwarfs have been detected to date, mainly from direct imaging, their characterisation is difficult due to their faintness and model-dependent results. In the case of transiting brown dwarfs, however, it is possible to make direct high-precision observations. Aims. Our aim is to investigate the nature and formation of brown dwarfs by adding a new well-characterised object, in terms of its mass, radius and bulk density, to the currently small sample of less than 20 transiting brown dwarfs. Methods. One brown dwarf candidate was found by the KESPRINT consortium when searching for exoplanets in the K2 space mission Campaign 16 field. We combined the K2 photometric data with a series of multicolour photometric observations, imaging, and radial velocity measurements to rule out false positive scenarios and to determine the fundamental properties of the system. Results. We report the discovery and characterisation of a transiting brown dwarf in a 5.17-day eccentric orbit around the slightly evolved F7V star EPIC 212036875. We find a stellar mass of 1.15 +/- 0.08 M-circle dot, a stellar radius of 1.41 +/- 0.05 R-circle dot, and an age of 5.1 +/- 0.9 Gyr. The mass and radius of the companion brown dwarf are 51 +/- 2 M-J and 0.83 +/- 0.03 R-J, respectively, corresponding to a mean density of 108(-13)(+15) g cm(-3). Conclusions. EPIC 212036875 b is a rare object that resides in the brown-dwarf desert. In the mass-density diagram for planets, brown dwarfs, and stars, we find that all giant planets and brown dwarfs follow the same trend from similar to 0.3 M-J to the turn-over to hydrogen burning stars at similar to 73 M-J. EPIC 212036875 b falls close to the theoretical model for mature H/He dominated objects in this diagram as determined by interior structure models. We argue that EPIC 212036875 b formed via gravitational disc instabilities in the outer part of the disc, followed by a quick migration. Orbital tidal circularisation may have started early in its history for a brief period when the brown dwarf's radius was larger. The lack of spin-orbit synchronisation points to a weak stellar dissipation parameter (Q(star)' greater than or similar to 10(8)), which implies a circularisation timescale of greater than or similar to 23 Gyr, or suggests an interaction between the magnetic and tidal forces of the star and the brown dwarf.
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