Binaries discovered by the SPY project

IV. Five single-lined DA double white dwarfs

¹ Department of Astrophysics, Radboud University Nijmegen, PO Box 9010 6500 GL, Nijmegen, The Netherlands e-mail: nelemans@astro.ru.nl
² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
³ Centre for Astrophysics Research, University of Hertfordshire, Hatfield, AL10 9AB, UK
⁴ Remeis-Sternwarte, Universität Erlangen-Nürnberg, Sternwartestr. 7, 96049 Bamberg, Germany
⁵ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁶ Institut für Theoretische Physik und Astrophysik, University of Kiel, 24098 Kiel, Germany
⁷ The Carolune Institute for Quality Astronomy, , UK
⁸ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁹ Hamburger Sternwarte, Universität Hamburg, Gojensbergweg 112, 21029 Hamburg, Germany

Received: 1 April 2005
Accepted: 6 June 2005

Abstract

We present results from our ongoing follow-up observations of double white dwarf binaries detected in the ESO SN Ia Progenitor SurveY (SPY). We discuss our observing strategy and data analysis and present the orbital solutions of five close double white dwarf binaries: HE0320-1917, HE1511-0448, WD0326-273, WD1013-010 and WD1210+140. Their periods range from 0.44 to 3.22 days. In none of these systems we find any spectral lines originating from the companion. This rules out main sequence companions and indicates that the companion white dwarfs are significantly older and cooler than the bright component. Infrared photometry suggests the presence of a cool, helium-rich white dwarf companion in the binary WD 0326-273. We briefly discuss the consequences of our findings for our understanding of the formation and evolution of double white dwarfs.