  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+-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 12C/13C. Values of the 12C/13C ratio
were obtained from a spectrum synthesis analysis. The derived 12C/13C 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 12C/13C, mass, metallicity and evolutionary
status.
