Circumstellar dust shells of carbon stars resolved with ISO

Abstract

We present far-infrared images of very extended dust shells of carbon stars observed with ISOPHOT on board the Infrared Space Observatory. A prototypical J-type carbon star Y CVn is surrounded by a very extended, detached dust shell, which shows that once there was a period with an intense mass-loss on the order of 10 −5 M Θ yr −1 followed by a swift switch to a phase with a mass-loss rate lower by two orders of magnitude about (1–2)×10 4 years ago. An N-type carbon star U Ant shows a double shell structure, a compact but resolved dust shell surrounded by a very extended one. The observed structure as well as the previously known thin CO gas shell indicates that this star experienced two cycles of “a high mass-loss phase of the order of 10 −5 M Θ yr −1 followed by a phase with a fainter mass-loss by two orders of magnitude” in the last (1–2)×10 4 years.