Post-common-envelope binaries from SDSS. XIII: Mass dependencies of the orbital period distribution

TL;DR

This study analyzes the orbital period distributions of post-common-envelope binaries from SDSS, revealing differences based on white dwarf core type and secondary star mass, providing new constraints for common-envelope evolution models.

Contribution

It offers the first detailed comparison of orbital periods for He- and C/O-core white dwarf PCEBs, highlighting mass dependencies and challenging recent theoretical predictions.

Findings

He-core PCEBs have significantly shorter orbital periods than C/O-core PCEBs.

Systems with more massive secondaries tend to have longer orbital periods.

Results impose new constraints on models of common-envelope evolution.

Abstract

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. 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. We performed standard statistical tests to compare the orbital period distributions and to determine the confidence levels of possible relations. 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 Porb ~ 0.28 d, the median orbital period for PCEBs containing C/O-core WDs is Porb ~ 0.57 d. We also find that systems containing more massive secondaries have longer post-CE orbital periods, in contradiction to recent predictions. 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.