Estimating the binary fraction of planetary nebulae central stars

TL;DR

This paper reviews methods for detecting binary central stars in planetary nebulae, emphasizing infrared excess observations to estimate the overall binary fraction and understand their role in nebula morphology.

Contribution

It introduces recent results using infrared excess techniques to detect binaries of all separations, advancing the estimation of the binary fraction among CSPN.

Findings

Infrared excess methods can detect wider binary systems.

Approximately 45 binary CSPN have been identified.

Infrared observations help estimate the true binary fraction.

Abstract

During the past 20 years, the idea that non-spherical planetary nebulae (PN) may need a binary or planetary interaction to be shaped was discussed by various authors. It is now generally agreed that the varied morphologies of PN cannot be fully explained solely by single star evolution. Observationally, more binary central stars of planetary nebulae (CSPN) have been discovered, opening new possibilities to understand the connections between binarity and morphology. So far, \simeq 45 binary CSPN have been detected, most being close systems detected via flux variability. To determine the PN binary fraction, one needs a method to detect wider binaries. We present here recent results obtained with the various techniques described, concentrating on binary infrared excess observations aimed at detecting binaries of any separation.