Chemical composition of evolved stars in the open cluster IC 4651

TL;DR

This study analyzes high-resolution spectra of evolved stars in IC 4651 to determine detailed chemical abundances, revealing specific elemental depletion and enrichment patterns compared to the Sun and Galactic disk stars.

Contribution

It provides the first detailed chemical abundance analysis of core-helium-burning and giant stars in IC 4651, including C, N, O, and isotope ratios, using high-resolution spectroscopy.

Findings

Carbon is depleted by about 0.3 dex.

Nitrogen is overabundant by about 0.2 dex.

Oxygen abundance is close to solar.

Abstract

We present an analysis of high-resolution spectra of three core-helium-burning "clump" stars and two first ascent giants in the open cluster IC 4651. Atmospheric parameters (T_eff, log_g, v_t, and [Fe/H]) were determined in our previous study by Carretta et al. (2004). In this study we present abundances of C, N, O and up to 24 other chemical elements. Abundances of carbon were derived using the C_2 Swan (0,1) band head at 5635.5 A. The wavelength interval 7980-8130 A, with strong CN features, was analysed in order to determine nitrogen abundances and 12^C/13^C isotope ratios. The oxygen abundances were determined from the [O i] line at 6300 A. Compared with the Sun and other dwarf stars of the Galactic disk, mean abundances in the investigated clump stars suggest that carbon is depleted by about 0.3 dex, nitrogen is overabundant by about 0.2 dex and oxygen is close to solar. This has the effect of lowering the mean C/N ratio to 1.36 +- 0.11. The mean 12^C/13^C ratios are lowered to 16 +- 2. Other investigated chemical elements have abundance ratios close to the solar ones.