Three new identifications of extended UV emission around AGB stars

Abstract

Asymptotic giant branch (AGB) stars experience heavy episodes of mass-loss through a slow stellar wind during the thermal pulse phase that form large, pc-scale structures around them. As the AGB stellar wind interacts with the interstellar medium (ISM), the otherwise isotropic ejecta gets distorted, resulting in asymmetric shapes, bow-shock structures and, in the case of fast motion relative to the surrounding ISM, extended wakes and tails as unexpectedly detected in GALEX ultraviolet (UV) images of o Cet, a.k.a. Mira. Since that discovery, another fourteen AGB stars have been reported to exhibit extended UV emission around them. Here we present the discovery of extended UV emission around another three AGB stars, namely R For, R Hor, and DM Tuc. The analysis of the overall properties of the regions of extended UV emission indicates that these are preferentially detected in closer AGB stars far away from the Galactic plane, i.e. sources less extincted. Faster AGB stars tend to have more elongated shapes, with bow-shocks and wakes or tails of material, while AGB stars farther away from the Galactic plane tend to be surrounded by larger regions of UV emission.