The determination of carbon and oxygen abundances in very metal-poor globular cluster giant stars

Abstract

The Anglo-Australian Telescope has been used to obtain spectra in the 2 μm region for two giant stars in the very metal-poor globular cluster NGC 6397. The spectra show that the CO bands are very weak. Analysis of these bands indicates that the carbon abundances are very low, e.g. [C/Fe]∼ -0.8, confirming the results from an earlier analysis of the CH bands. In addition, the CO analysis gives oxygen abundances of [O/Fe]∼ -0.4±0.4, in disagreement with analyses of extreme population II subdwarfs and halo giants, but in better agreement with results from high dispersion spectroscopy of some giants in two other low metallicity globular clusters. Show more