Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aj....122.2554k&link_type=abstract
The Astronomical Journal, Volume 122, Issue 5, pp. 2554-2560.
Astronomy and Astrophysics
Astronomy
18
Stars: Abundances, Stars: Evolution, Stars: Population Ii
Scientific paper
We have estimated 12C/13C in 15 metal-poor (-2.4<=[Fe/H]<=-1.0) field halo giant stars from spectra of the 13CO v=3-1 and v=2-0 band heads and surrounding 12CO and 13CO R-branch lines. Our isotope ratios are consistent with previous measurements for stars in our sample with 12C/13C determined either from the infrared first-overtone bands of CO or from optical G-band spectra of CH and red system bands of CN. We have also compiled carbon isotope ratios from the literature for a much larger sample of field and cluster red giant branch (RGB) stars spanning a wide range of metallicities (-2.4<=[Fe/H]<=solar). Combining these data, we confirm the decline of the isotope ratio as stars evolve up the RGB and we have identified a trend toward higher levels of mixing in more metal-poor stars. Standard RGB first dredge-up models do not predict the carbon isotope ratios that we observe in the more evolved (higher luminosity) metal-poor stars, but more recent models that account for other mixing mechanisms can explain these data; even for very metal-poor stars such as those that we have observed in the Galactic halo.
Keller Luke D.
Pilachowski Catherine A.
Sneden Christopher
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