Ongoing surveys for close binary central stars and wider implications

TL;DR

Recent large-scale surveys have increased the known close binary central stars in planetary nebulae, revealing trends that inform stellar evolution, nebula shaping, and binary interaction processes.

Contribution

This paper reports on ongoing surveys that significantly expand the sample of binary central stars and explore their implications for planetary nebulae morphology and evolution.

Findings

At least 20% of PNe have close binary nuclei.

Post-CE nebulae often show bipolar shapes and low-ionisation structures.

New binary discoveries reinforce the link between binaries and nebula features.

Abstract

Binary central stars have long been invoked to explain the vexing shapes of planetary nebulae (PNe) despite there being scant direct evidence to support this hypothesis. Modern large-scale surveys and improved observing strategies have allowed us to significantly boost the number of known close binary central stars and estimate at least 20% of PNe have close binary nuclei that passed through a common-envelope (CE) phase. The larger sample of post-CE nebulae appears to have a high proportion of bipolar nebulae, low-ionisation structures (especially in SN1987A-like rings) and polar outflows or jets. These trends are guiding our target selection in ongoing multi-epoch spectroscopic and photometric surveys for new binaries. Multiple new discoveries are being uncovered that further strengthen the connection between post-CE trends and close binaries. These ongoing surveys also have wider implications for understanding CE evolution, low-ionisation structure and jet formation, spectral classification of central stars, asymptotic giant branch (AGB) nucleosynthesis and dust obscuration events in PNe.