Carbon isotope ratio in carbon stars of the galactic halo.

Details Carbon isotope ratio in carbon stars of the galactic halo. Carbon isotope ratio in carbon stars of the galactic halo.

Feb 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...317..845a&link_type=abstract

Astronomy and Astrophysics, v.317, p.845-858

Astronomy and Astrophysics

Astrophysics

20

Stars: Abundances, Stars: Carbon, Stars: Population Ii, Stars: Agb And Post Agb, Galaxy: Halo

Scientific paper

We analysed CN red system (~8000Å) and C_2_ Swan system (~4700Å) to know carbon isotope ratios (^12^C/^13^C) for carbon stars in the Galactic halo, named CH stars. The isotope ratios are obtained for 6 CH stars by the curve-of-growth analysis of the isolated ^12^CN and ^13^CN lines. In this analysis, we compared directly ^12^CN and ^13^CN lines of similar intensities (iso-intensity method), and the resulting ^12^C/^13^C ratios are almost independent of the model atmosphere and its parameters. The ^13^CN lines appear to be too weak in some CH stars, for which we applied the spectral synthesis method to the stronger C_2_ Swan band, obtained ^12^C/^13^C ratios for two stars and estimated the lower limits of ^12^C/^13^C ratios for two stars. In this case, however, the results depend on model atmosphere and its parameters. Results from our present and previous works show that most of them (12 stars) distribute around ^12^C/^13^C~10 and two stars have very high values (^12^C/^13^C>=500). The distribution of ^12^C/^13^C ratios in CH stars is different from that of the population I carbon stars as well as population II oxygen-rich giants (G~K types). The CH stars of very high ^12^C/^13^C ratios can be explained by dredge-up of ^12^C due to 3α-process as in population I carbon stars (N-type). On the other hand the formation of the CH stars with low ^12^C/^13^C ratios requires the large supply of ^12^C followed by a process of decreasing ^12^C/^13^C ratio.

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