RESOLUTION OF A FOSSIL DUST SHELL AROUND U-HYDRAE USING MAXIMUM-ENTROPY IMAGE-RECONSTRUCTION

High resolution image reconstruction techniques applied to the 60 and 100 mum data obtained with the InfraRed Astronomical Satellite reveal the presence of a detached ring of dust around the evolved carbon-rich star U Hydrae. The ring is clearly resolved at 60 mum but only margin ally at 100 mum. The 60 mum image provides the first direct evidence t hat the far-IR excess associated with cool carbon stars is due to a pr evious episode of high mass loss. The age of the fossil shell is estim ated at 12,000 yrs and the mass loss rate at 5 10(-6) M. yr-1. This is about a factor 25 higher than the present-day mass loss rate. It is c oncluded that the mass loss rate of carbon stars on the Asymptotic Gia nt Branch is variable on a timescale that is compatible with the therm al pulse timescale of intermediate mass stars in that evolutionary pha se. The Groningen IRAS data reduction system runs within GIPSY and is available to outside users.