Greening of the brown-dwarf desert. EPIC 212036875b: a 51 MJ object in a 5-day orbit around an F7 V star

Research output: Contribution to journalArticle

Abstract

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 F7 V star EPIC 212036875. We find a stellar mass of 1.15 ± 0.08 M, a stellar radius of 1.41 ± 0.05 R, and an age of 5.1 ± 0.9 Gyr. The mass and radius of the companion brown dwarf are 51 ± 2 MJ and 0.83 ± 0.03 RJ, respectively, corresponding to a mean density of 108+15-13 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 0.3 MJ to the turn-over to hydrogen burning stars at 73 MJ. 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*' ≳ 108), which implies a circularisation timescale of ≳23 Gyr, or suggests an interaction between the magnetic and tidal forces of the star and the brown dwarf. Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A64This work is done under the framework of the KESPRINT collaboration (http://kesprint.science). KESPRINT is an international consortium devoted to the characterisation and research of exoplanets discovered with space-based missions.

Details

Authors
  • Carina M. Persson
  • Szilárd Csizmadia
  • Malcolm Fridlund
  • Artie P. Hatzes
  • Grzegorz Nowak
  • Iskra Georgieva
  • Davide Gandolfi
  • John H. Livingston
  • Enric Palle
  • Pilar Montañes Rodriguez
  • Michael Endl
  • Teruyuki Hirano
  • Jorge Prieto-Arranz
  • Judith Korth
  • Sascha Grziwa
  • Massimiliano Esposito
  • Simon Albrecht
  • Marshall C. Johnson
  • Oscar Barragán
  • Hannu Parviainen
  • Vincent Van Eylen
  • Roi Alonso Sobrino
  • Paul G. Beck
  • Juan Cabrera
  • Ilaria Carleo
  • William D. Cochran
  • Fei Dai
  • Hans J. Deeg
  • Jerome P. de Leon
  • Philipp Eigmüller
  • Anders Erikson
  • Akai Fukui
  • Lucia González-Cuesta
  • Eike W. Guenther
  • Diego Hidalgo
  • Maria Hjorth
  • Petr Kabath
  • Emil Knudstrup
  • Nobuhiko Kusakabe
  • Kristine W.~F. Lam
  • Mikkel N. Lund
  • Rafael Luque
  • Savita Mathur
  • Felipe Murgas
  • Norio Narita
  • David Nespral
  • Prajwal Niraula
  • A.~O. Henrik Olofsson
  • Martin Pätzold
  • Heike Rauer
  • Seth Redfield
  • Ignasi Ribas
  • Marek Skarka
  • Alexis M.~S. Smith
  • Jan Subjak
  • Motohide Tamura
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Astronomy, Astrophysics and Cosmology

Keywords

  • planetary systems, stars: fundamental parameters, stars: individual: EPIC 212036875, techniques: photometric, techniques: radial velocities, Astrophysics - Earth and Planetary Astrophysics
Original languageEnglish
Pages (from-to)A64
JournalAstronomy & Astrophysics
Volume628
Publication statusPublished - 2019 Aug 1
Publication categoryResearch
Peer-reviewedYes

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