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Astron. Astrophys. 346, 520-522 (1999)

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On the determination of carbon isotopic ratios in cool carbon stars

II. Accuracy of the iso-intensity method for crowded spectra

P. de Laverny 1 and B. Gustafsson 2

1 Observatoire de la Côte d'Azur, Département Fresnel UMR 6528, B.P. 4229, F-06304 Nice, France
2 Astronomiska Observatoriet, Box 515, S-751 20 Uppsala, Sweden

Received 5 March 1999 / Accepted 26 March 1999


de Laverny & Gustafsson (1998, Paper I) questioned the iso-intensity method used by Ohnaka & Tsuji (1996) to derive carbon isotopic ratios in cool carbon stars. As a reply, Ohnaka & Tsuji (1998) pointed out that the method criticized in Paper I differs from the original one and conclude that our results are unreliable. No comparison of the two methods was, however, made. The iso-intensity method used in Paper I and OT96 do slighty differ in their definition. In investigating the consequences of this difference we have found that they are rather insignificant. We therefore confirm that the iso-intensity method is not reliable when applied to crowded spectra of cool stars. That reinforces the conclusions presented in Paper I.

Key words: stars: abundances – stars: late-type – stars: AGB and post-AGB – stars: carbon – molecular processes

Send offprint requests to: P. de Laverny (laverny@obs-nice.fr)

© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999