Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...332..661d&link_type=abstract
Astronomy and Astrophysics, v.332, p.661-671 (1998)
Astronomy and Astrophysics
Astrophysics
25
Stars: Abundances, Stars: Agb And Post-Agb, Stars: Carbon, Molecular Processes
Scientific paper
We discuss the determination of carbon isotopic ratios (12C) / (12C) iso in N-type Galactic carbon stars. Ohnaka & Tsuji (1996) reported (12C) / (12C) iso ratios smaller by a factor 2 or 3 than the determinations of Lambert et al. (1986). Using synthetic spectra of carbon stars, we analyse systematic errors in their iso-intensity method. It is found to be rather sensitive to model parameters and blends. Furthermore, there are large discrepancies between the effective temperatures adopted by these two studies (mean discrepancy close to 260 K for the 20 stars in common). That, together with uncertainties due to model atmospheres, to carbon enrichments and effects of the blends, could explain most of the discrepancies between these two studies. The LGEH86 analysis is, on the other hand, rather insensitive to model parameters. We therefore conclude that large (12C) / (12C) iso ratios in cool Galactic carbon stars should be favoured.
de Laverny Patrick
Gustafsson Bengt
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