SIMBAD references

Investigations of abundances of carbon and nitrogen in the atmospheres of evolved stars of open clusters may provide comprehensive information on chemical composition changes caused by stellar evolution. Our main aim is to increase the number of open clusters with determined carbon-to nitrogen and carbon isotope ratios. High-resolution spectra were analysed using a differential model atmosphere method. Abundances of carbon were derived using the C₂ Swan (0, 1) band head at 5635.5Å (FEROS spectra) and the C₂ Swan (1, 0) band head at 4737Å (UVES spectra). The wavelength interval 7980-8130Å, with strong CN features was analysed to determine nitrogen abundances and ¹²C/¹³C isotope ratios. The oxygen abundances were determined from the [Oi] line at 6300Å. The average value of ¹²C/¹³C isotope ratios of Cr261 is equal to 18±2 in four giants and to 12±1 in two clump stars; it is equal to 16±1 in four clump stars of the open cluster NGC6253. The mean C/N ratios in Cr261 and NGC6253 are equal to 1.67±0.06 and 1.37±0.09, respectively. The ¹²C/¹³C and C/N values in Cr261 and NGC6253 within limits of uncertainties agree with the theoretical model of thermohaline-induced mixing as well as with the cool-bottom processing model.