We present the discovery of a huge (19' x 16') dust ring surrounding a bright (V = 10.60) red star. The dust ring has, at D = 700 pc, a diameter of 4 pc and a central hole of ～1.5 pc across. Part of the shell is also seen as an absorption nebulosity. The star is classified as an M3 III asymptotic giant branch (AGB) star. Among AGB stars, its detached shell is of unrivaled size. Detached shells around AGB stars are normally interpreted in terms of thermal pulses. However, in this case, a significant fraction of the shell may consist of swept-up ISM; the detached appearance can be explained with wind-ISM interaction. We present a model in which the AGB wind has been stopped by the surrounding ISM and the swept-up shell is now expanding at the sound speed. The model predicts that the ring will disperse over a few times 10~5 yr and eventually will leave a large hole in the ISM surrounding the AGB star or its future planetary nebula.
展开▼
