EXTENDED DUST SHELLS AROUND CARBON STARS RESOLVED BY HIRAS

We have examined forty-two carbon stars which show excess emission at 60 and/or 100 mu m by applying maximum-entropy image reconstruction te chniques to the IRAS 60 mu m survey data. Thirteen stars are found to be extended in the reconstructed images. Four of them show a detached ring centered on the stellar position. In particular, U Ant may have a double detached dust shell. The implications of our results are discu ssed concerning the variation of mass loss on the AGB evolution.