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Nucleosynthesis in AGB stars: Observation of Mg and Mg in IRC+10216 and possible detection of Al

M. Guélin, M. Forestini, P. Valiron, L. M. Ziurys, M.A. Anderson, J. Cernicharo, C. Kahane
IRAM, 300 rue de la piscine, F-38406 S Martin d'Hères, France
Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, F-38041 S Martin d'Hères Cedex 09, France
Arizona State University, Dept. of Chemistry, Tempe, AZ 85287-1604, USA
Centro Astronomico de Yebes, IGN, E-19080 Guadalajara, Spain
Abstract: We report the detection in the circumstellar envelope IRC+10216 of millimeter lines of the rare isotopomers NC and NC, as well as of a line at 234433 MHz, which could be the J= 7--6 transition of F (an alternate, although less likely identification would be the J= 9--8 transition of NaF). The derived :: isotopic abundance ratios () are consistent with the solar system values (78.7:10.1:11.2). According to new calculations of evolutionary models of and AGB stars, these ratios and the previously measured N, O and Si isotopic ratios imply that the central star had an initial mass and has already experienced many 3 dredge-up events. From this, it can be predicted that the / isotopic ratio lies between 0.01 and 0.08; in fact, the value derived in the case U234433 arises from F is /= 0.04.

Figure: Two spectra, observed toward IRC+10216 with the IRAM 30-m telescope, and covering the frequencies of the J= 7--6 transitions of F (top) and F (bottom). The channel width is 1 MHz. The position and strength of the F line hyperfine components are denoted by vertical lines. U234433 lies only 0.9 MHz below the calculated frequency of F (7--6) and could well be this line; an alternate, but less likely identification is the J= 9--8 line of NaF, the rest frequency of which is 234435.2 MHz.

Figure: The N= 7--6 through N= 9--8 rotational lines of NC in IRC+10216. The channel width is 1 MHz

The identification of the NC and NC lines was made possible by ab-initio quantum mechanical calculations of the molecule geometrical structure. It was confirmed through millimeter-wave laboratory measurements. The quantum mechanical calculations are briefly described and the laboratory results presented in some detail. The rotation constants B, D, H and the spin-rotation constant of NC and NC, and the hyperfine constants b and eqQ of NC are determined from a fit of laboratory and astronomical data.

Accepted by Astronomy and Astrophysics
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Next: CO in the Up: Scientific Results Previous: Scientific Results

Robert Lucas
Thu Mar 9 12:42:24 MET 1995