, P. Bergman 
, R. Lucas 
,
K. Eriksson 
, B. Gustafsson , J.H.Bieging 
Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden Onsala Space Observatory, S-439 92 Onsala, Sweden Institut de RadioAstronomie Millimétrique, 300
rue de la Piscine, F-38406 Saint Martin d'Hères, France Uppsala Astronomical Observatory, Box 515, S-751 20 Uppsala, Sweden Steward Observatory, Univ. of Arizona, Tucson, AZ 85721, USA
Figure: CO (J=1-0 and 2-1) maps of TT Cyg averaged over the
interval 
. The star and about a quarter of the shell
have been covered. The intensity unit is Jy beam 
.
Interferometric CO(J=1-0 and 2-1) observations reveal a remarkably
thin shell of molecular gas around the carbon star TT Cyg,
width/radius 
(Fig. 1).
It expands at 
13 
, and contains 
of gas
provided the CO abundance with respect to H 
is 10 
and the
distance is 1 kpc. The overall geometry is spherically symmetric,
but clear deviations, at the per cent level, exist. The radial
structure of the shell is barely resolved at the arc second level,
but there exists weak emission extending a few arc seconds inwards
from the peak. A drastic change in mass loss properties, possibly
combined with the effects of interacting winds, provides the most
likely explanation to the origin of the shell.
