Carbon isotope ratios , along with carbon and nitrogen abundances , are derived in a sample of 11 red-giant members of one of the most metal-rich clusters in the Milky Way , NGC 6791 .
The selected red-giants have a mean metallicity and standard deviation of [ Fe/H ] =+0.39 \pm 0.06 ( Cunha et al .
2015 ) .
We used high resolution H-band spectra obtained by the SDSS-IV Apache Point Observatory Galactic Evolution Experiment ( APOGEE ) .
The advantage of using high-resolution spectra in the H-band is that lines of CO are well represented and their line profiles are sensitive to the variation of ^ { 12 } C/ ^ { 13 } C. Values of the ^ { 12 } C/ ^ { 13 } C ratio were obtained from a spectrum synthesis analysis .
The derived ^ { 12 } C/ ^ { 13 } C ratios varied between 6.3 and 10.6 in NGC 6791 , in agreement with the final isotopic ratios from thermohaline-induced mixing models .
The ratios derived here are combined with those obtained for more metal poor red-giants from the literature to examine the correlation between ^ { 12 } C/ ^ { 13 } C , mass , metallicity and evolutionary status .