Post common envelope binaries from SDSS

XII. The orbital period distribution^⋆,⋆⋆

¹ Université de Strasbourg, CNRS, UMR 7550, Observatoire Astronomique de Strasbourg, 11 rue de l’Université, 67000 Strasbourg, France
e-mail: ada.nebot@astro.unistra.fr
² Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁴ Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
⁵ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁶ Department of Physics, Faculty of Science, Naresuan University, 65000 Phitsanulok, Thailand
⁷ ThEP Centre, CHE, 328 Si Ayutthaya Road, 10400 Bangkok, Thailand
⁸ Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP226, Boulevard du Triomphe, 1050, Belgium
⁹ Open University, Dept. Physics & Astronomy, Milton Keynes MK7 6BJ, UK
¹⁰ Institute of Astronomy & Astrophysics, National Observatory of Athens, 15236 Athens, Greece
¹¹ Instituto de Astrofísica de Canarias, vía Láctea, s/n, La Laguna, 38205 Tenerife, Spain
¹² Departamento de Astrofísica, Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez, sn, La Laguna, 38206 Tenerife, Spain
¹³ Isaac Newton Group of Telescopes, Apartado de correos 321, S/C de la Palma, 38700 Canary Islands, Spain
¹⁴ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
¹⁵ Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica, Vicuña Mackenna 4860, 782-0436 Macul, Chile

Received: 17 June 2011
Accepted: 20 September 2011

Abstract

Context. The complexity of the common-envelope phase and of magnetic stellar wind braking currently limits our understanding of close binary evolution. Because of their intrinsically simple structure, observational population studies of white dwarf plus main sequence (WDMS) binaries can potentially test theoretical models and constrain their parameters.

Aims. The Sloan Digital Sky Survey (SDSS) has provided a large and homogeneously selected sample of WDMS binaries, which we characterise in terms of orbital and stellar parameters.

Methods. We have obtained radial velocity information for 385 WDMS binaries from follow-up spectroscopy and for an additional 861 systems from the SDSS subspectra. Radial velocity variations identify 191 of these WDMS binaries as post common-envelope binaries (PCEBs). Orbital periods of 58 PCEBs were subsequently measured, predominantly from time-resolved spectroscopy, bringing the total number of SDSS PCEBs with orbital parameters to 79. Observational biases inherent to this PCEB sample were evaluated through extensive Monte Carlo simulations.

Results. We find that 21–24% of all SDSS WDMS binaries have undergone common-envelope evolution, which is in good agreement with published binary population models and high-resolution HST imaging of WDMS binaries unresolved from the ground. The bias-corrected orbital period distribution of PCEBs ranges from 1.9 h to 4.3 d and approximately follows a normal distribution in log (P_orb), peaking at  ~10.3 h. There is no observational evidence for a significant population of PCEBs with periods in the range of days to weeks.

Conclusions. The large and homogeneous sample of SDSS WDMS binaries provides the means to test fundamental predictions of binary population models, hence to observationally constrain the evolution of all close compact binaries.