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Astron. Astrophys. 317, 883-888 (1997)


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Research Note

14C in AGB stars: the case of IRC+10216

M. Forestini 1, M. Guélin 2 and J. Cernicharo 3

1 Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, BP 53, F-38041 [FORMULA] Martin d'Hères Cedex 9, France
2 IRAM, 300 Rue de la piscine, F-38406 [FORMULA] Martin d'Hères, France
3 Observatorio Astronomico Nacional, apartado 1143, E-28800 Alcalá de Henares, Spain

Received 21 February 1996 / Accepted 31 May 1996

Abstract

Observations and stellar evolution computations have been dedicated to the search for [FORMULA] in the archetype of AGB stars, IRC+10216/CW Leo. Contrary to Wright's (1994) tentative detection, we see no trace of [FORMULA] in this star down to a [FORMULA] limit [FORMULA] [FORMULA] / [FORMULA] [FORMULA]. The new limit is consistent with our stellar evolution computations, which indicate that R should be [FORMULA]. Comparison of the C, N, O, Mg, Si, and S isotopic ratios observed in this source with the calculated ones reinforces our earlier conclusion that CW Leo had a main sequence mass [FORMULA] [FORMULA] [FORMULA] (see Guélin et al. 1995).

While searching for the [FORMULA] 2-1 line, we detected the (1 [FORMULA]) [FORMULA] line of vibrationally excited SiC2. The latter line pertains to the first vibrational level of the [FORMULA] bending state and its upper level has an energy of 290 K, lower than the temperature of the dust forming shell. The line has a pyramidal shape and shows acceleration steps, which we interpreted in terms of dust formation.

Key words: stars: AGB – stars: IRC +10216 – nucleosynthesis – stars: abundances – molecular data – radio lines: stars

Send offprint requests to: M. Forestini

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998

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