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Astron. Astrophys. 320, 249-256 (1997)

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Superwind in evolved OH/IR stars

X. Delfosse , C. Kahane and T. Forveille

Observatoire de Grenoble, B.P. 53, F-38041 Grenoble Cedex 9, France (delfosse@gag.observ-gr.fr; kahane@gag.observ-gr.fr; forveill@gag.observ-gr.fr;)

Received 22 July 1996 / Accepted 13 September 1996


We report observations of 13 CO (J=1-0) and (J=2-1) emission towards 5 evolved OH/IR envelopes. Four of them are known to have very weak CO emission compared to their infrared flux, and an anomalously high (J=2-1)/(J=1-0) intensity ratio. Modeling of their 12 CO and 13 CO lines is used to test several possible explanations of this behaviour. We conclude that it is most likely due to the recent onset of a superwind phase. Another interesting result of the modeling is the very low 12 C/13 C isotopic ratios we derive in these envelopes, of the order of 3.5 and close to the equilibrium value of the CNO cycle. We interpret this as the signature of massive stars at the end of their AGB phase. The sixth envelope, which shows a much lower (J=2-1)/(J=1-0) intensity ratio, also has a low, marginally larger, 12 C/13 C isotopic ratio. We conclude that it also is a massive object, but in a slightly less evolved stage, just before the superwind phase.

Key words: stars: circumstellar matter – stars: AGB, post-AGB – stars: mass loss – radio lines: stars

Send offprint requests to: X. Delfosse

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998