Equivalent widths of 13 red giants in IC 4756

Homogeneous investigations of red giant stars in open clusters contribute to studies of internal evolutionary mixing processes inside stars, which are reflected in abundances of mixing-sensitive chemical elements like carbon, nitrogen, and sodium, while {alpha}- and neutron-capture element abundances are useful in tracing the Galactic chemical evolution. The main aim of this study is a comprehensive chemical analysis of red giant stars in the open cluster IC 4756, including determinations of ^12^C/^13^C and C/N abundance ratios, and comparisons of the results with theoretical models of stellar and Galactic chemical evolution.

We used a classical differential model atmosphere method to analyse high-resolution spectra obtained with the FEROS spectrograph on the 2.2m MPG/ESO Telescope. The carbon, nitrogen, and oxygen abundances, ^12^C/^13^C ratios, and neutron-capture element abundances were determined using synthetic spectra, and the main atmospheric parameters and abundances of other chemical elements were determined from equivalent widths of spectral lines.