Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse

TL;DR

This study uses ultraviolet imaging to detect hot binary companions in cool AGB stars, revealing significant UV excesses that suggest binarity plays a key role in shaping planetary nebulae.

Contribution

First UV survey of AGB stars with GALEX to identify hot companions, providing new insights into binarity's role in stellar evolution.

Findings

Detected UV excesses in 9 AGB stars

UV excess likely indicates hot binary companions or accretion disks

Supports binarity's influence on planetary nebula morphology

Abstract

The search for binarity in AGB stars is of critical importance for our understanding of how planetary nebulae acquire the dazzling variety of aspherical shapes which characterises this class. However, detecting binary companions in such stars has been severely hampered due to their extreme luminosities and pulsations. We have carried out a small imaging survey of AGB stars in ultraviolet light (using GALEX) where these cool objects are very faint, in order to search for hotter companions. We report the discovery of significant far-ultraviolet excesses towards nine of these stars. The far-ultraviolet excess most likely results either directly from the presence of a hot binary companion, or indirectly from a hot accretion disk around the companion.