12C/13C isotopic ratios in red-giant stars of the open cluster NGC 6791

TL;DR

This study measures carbon isotope ratios in red giants of the metal-rich cluster NGC 6791 using high-resolution H-band spectra, providing insights into stellar mixing processes and chemical evolution.

Contribution

It presents the first detailed 12C/13C ratio measurements for red giants in NGC 6791 using APOGEE data, linking isotopic ratios with stellar evolution models.

Findings

12C/13C ratios range from 6.3 to 10.6.

Ratios agree with thermohaline mixing models.

Correlations with mass and metallicity are examined.

Abstract

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.