Letter to the Editor

Post common envelope binaries from SDSS

XIII. Mass dependencies of the orbital period distribution

¹ Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
e-mail: mzorotov@dfa.uv.cl
² Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Santiago, Chile
³ Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
⁴ Université de Strasbourg, CNRS, UMR 7550, Observatoire Astronomique de Strasbourg, 11 rue de l’Université, 67000 Strasbourg, France
⁵ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁶ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁷ Instituto de Astrofísica de Canarias, Vía Láctea, s/n, La Laguna, 38205 Tenerife, Spain
⁸ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁹ European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile

Received: 1 August 2011
Accepted: 8 November 2011

Abstract

Context. Post-common-envelope binaries (PCEBs) consisting of a white dwarf (WD) and a main-sequence secondary star are ideal systems to constrain models of common-envelope (CE) evolution. Until very recently, observed samples of PCEBs have been too small to fully explore this potential, however the recently identified large and relatively homogenous sample of PCEBs from the Sloan Digital Sky Survey (SDSS) has significantly changed this situation.

Aims. We here analyze the orbital period distributions of PCEBs containing He- and C/O-core WDs separately and investigate whether the orbital period of PCEBs is related to the masses of their stellar components.

Methods. We performed standard statistical tests to compare the orbital period distributions and to determine the confidence levels of possible relations.

Results. The orbital periods of PCEBs containing He-core WDs are significantly shorter than those of PCEBs containing C/O-core WDs. While the He-core PCEB orbital period distribution has a median value of P_orb ~ 0.28 d, the median orbital period for PCEBs containing C/O-core WDs is P_orb ~ 0.57 d. We also find that systems containing more massive secondaries have longer post-CE orbital periods, in contradiction to recent predictions.

Conclusions. Our observational results provide new constraints on theories of CE evolution. However we suggest future binary population models to take selection effects into account that still affect the current observed PCEB sample.