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Astron. Astrophys. 330, L1-L4 (1998)

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Letter to the Editor

A thin molecular shell around the carbon star TT Cyg

H. Olofsson 1, P. Bergman 2, R. Lucas 3, K. Eriksson 4, B. Gustafsson 4 and J.H. Bieging 5

1 Stockholm Observatory, S-133 36 Saltsjöbaden, Sweden
2 Onsala Space Observatory, S-439 92 Onsala, Sweden
3 IRAM, 300, rue de la Piscine, F-38406 Grenoble-Cedex, France
4 Uppsala Astronomical Observatory, Box 515, S-751 20 Uppsala, Sweden
5 Steward Observatory, University of Arizona, Tucson, AZ 85721, USA

Received 7 October 1997 / Accepted 24 October 1997

Abstract

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 [FORMULA] 1 [FORMULA] 3/34 [FORMULA] [FORMULA] 0.04. It expands at [FORMULA] 13 [FORMULA], and contains [FORMULA] 0.02 [FORMULA] of gas provided the CO abundance with respect to H2 is 10-3 and the distance is 1 kpc. Only about a quarter of the shell has been mapped, but we infer an overall spherical shell with only small, but clear, deviations at the per cent level. 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.

Key words: stars: carbon – circumstellar matter – stars: individual: TT Cyg – stars: mass-loss – radio lines: molecular: circumstellar

Send offprint requests to: H. Olofsson (e-mail: hans@astro.su.se)

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© European Southern Observatory (ESO) 1998

Online publication: January 8, 1998
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