The EBLM project

II. A very hot, low-mass M dwarf in an eccentric and long-period, eclipsing binary system from the SuperWASP Survey^⋆

¹ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
e-mail: y.gomez@warwick.ac.uk
² Institut d’Estudis Espacials de Catalunya (IEEC), Edif. Nexus, C/ Gran Capità 2-4, 08034 Barcelona, Spain
³ LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, France
⁴ Departamento de Física Aplicada I, E.T.S. Ingeniería, Universidad del País Vasco, 9 Alameda Urquijo s/n, 48013 Bilbao, Spain
⁵ Esteve Duran Observatory Foundation Fundació Observatori Esteve Duran, Avda. Montseny 46, 08553 Seva, Spain
⁶ Department of Physics, Hobart and William Smith Colleges, Geneva, New York 14456, USA
⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge MA 02138, USA
⁸ Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park PA 16802, USA
⁹ Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park PA 16802, USA
¹⁰ Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de Palma, Spain
¹¹ Astronomy Department, University of Washington, Seattle, Washington, USA
¹² Kavli Institute for Astrophysics & Space Research, Massachusetts Institute of Technology, Cambridge MA 02139, USA
¹³ Fellow of the Swiss National Science Foundation  
¹⁴ School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, UK
¹⁵ Department of Physics and Astronomy, N283 ESC, Brigham Young University, Provo UT 84602-4360, USA
¹⁶ Physics and Astronomy Department, Vanderbilt University, Nashville, Tennessee, USA
¹⁷ Department of Physics, Fisk University, Nashville TN 37208, USA
¹⁸ Instituto de Astrofísica de Canarias, C/Vía Láctea sn, 382000 La Laguna, Tenerife, Spain
¹⁹ Departamento de Astrofísica, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez sn, 38206 La Laguna, Spain

Received: 23 May 2014
Accepted: 28 August 2014

Abstract

In this paper, we derive the fundamental properties of 1SWASPJ011351.29+314909.7 (J0113+31), a metal-poor (−0.40 ± 0.04 dex), eclipsing binary in an eccentric orbit (~0.3) with an orbital period of ~14.277 d. Eclipsing M dwarfs that orbit solar-type stars (EBLMs), like J0113+31, have been identified from their light curves and follow-up spectroscopy in the course of the WASP transiting planet search. We present the analysis of the first binary of the EBLM sample for which masses, radii and temperatures of both components are derived, and thus, define here the methodology. The primary component with a mass of 0.945 ± 0.045 M_⊙ has a large radius (1.378±0.058 R_⊙) indicating that the system is quite old, ~9.5 Gyr. The M-dwarf secondary mass of 0.186 ± 0.010 M_⊙ and radius of 0.209 ± 0.011 R_⊙ are fully consistent with stellar evolutionary models. However, from the near-infrared secondary eclipse light curve, the M dwarf is found to have an effective temperature of 3922 ± 42 K, which is ~600 K hotter than predicted by theoretical models. We discuss different scenarios to explain this temperature discrepancy. The case of J0113+31 for which we can measure mass, radius, temperature, and metallicity highlights the importance of deriving mass, radius, and temperature as a function of metallicity for M dwarfs to better understand the lowest mass stars. The EBLM Project will define the relationship between mass, radius, temperature, and metallicityfor M dwarfs providing important empirical constraints at the bottom of the main sequence.