DE Canum Venaticorum: a bright, eclipsing red dwarf–white dwarf binary

¹ Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands e-mail: [besselaar;lmr;nelemans;pgroot]@astro.ru.nl
² Isaac Newton Group of Telescopes, Apartado de correos 321, 38700 Santa Cruz de la Palma, Spain e-mail: greimel@ing.iac.es
³ Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory Hanover, NH 03755, USA e-mail: thorsten@partita.dartmouth.edu
⁴ Department of Physics, University of Warwick, Coventry CV4 7AL, UK e-mail: t.r.marsh@warwick.ac.uk
⁵ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK e-mail: vik.dhillon@sheffield.ac.uk
⁶ Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 3P6, Canada e-mail: robb@uvic.ca; e-mail: cosmos@uvvm.uvic.ca
⁷ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: guenther@tls-tautenburg.de
⁸ Joint Astronomy Centre 660 N. A'ohoku Place University Park Hilo, Hawaii 96720, USA e-mail: j.kemp@jach.hawaii.edu
⁹ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain e-mail: tau@not.iac.es

Received: 14 August 2006
Accepted: 16 January 2007

Abstract

Context.Close white dwarf–red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf–red dwarf binary with a relatively short (~8.7 h) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study.

Aims.From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters that we discuss in the framework of common-envelope evolution.

Methods.Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average low-resolution spectrum of DE CVn, we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system.

Results.The derived ephemeris is HJD_min = 2 452 784.5533(1) + 0.3641394(2) . The red dwarf in DE CVn has a spectral type of M3V and the white dwarf has an effective temperature of K. The inclination of the system is and the mass and radius of the red dwarf are and , respectively, and the mass and radius of the white dwarf are and , respectively.

Conclusions.We found that the white dwarf has a hydrogen-rich atmosphere (DA-type). Given that DE CVn has experienced a common-envelope phase, we can reconstruct its evolution and we find that the progenitor of the white dwarf was a relatively low-mass star (). The current age of this system is years, while it will take longer than the Hubble time for DE CVn to evolve into a semi-detached system.