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A thin molecular shell around the carbon star TT Cyg

H Olofsson tex2html_wrap_inline729 , P. Bergman tex2html_wrap_inline731 , R. Lucas tex2html_wrap_inline733 , K. Eriksson tex2html_wrap_inline735 , B. Gustafsson tex2html_wrap_inline735 , J.H.Bieging tex2html_wrap_inline739
tex2html_wrap_inline729 Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden
tex2html_wrap_inline731 Onsala Space Observatory, S-439 92 Onsala, Sweden
tex2html_wrap_inline733 Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France
tex2html_wrap_inline735 Uppsala Astronomical Observatory, Box 515, S-751 20 Uppsala, Sweden
tex2html_wrap_inline739 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 tex2html_wrap_inline671 . The star and about a quarter of the shell have been covered. The intensity unit is Jy beam tex2html_wrap_inline603 .

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 tex2html_wrap_inline655 (Fig. 1). It expands at tex2html_wrap_inline657 13 tex2html_wrap_inline659 , and contains tex2html_wrap_inline661 of gas provided the CO abundance with respect to H tex2html_wrap_inline663 is 10 tex2html_wrap_inline665 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.