2011MNRAS.416.1092M

In this study we present abundances of ¹²C, ¹³C, N, O and up to 26 other chemical elements in two first-ascent giants and two core-helium-burning `clump' stars of the open cluster NGC 2506. Abundances of carbon were derived using the C₂ Swan (0,1) band head at 5635.5 Å. The wavelength interval 7940–8130 Å, with strong CN features, was analysed in order to determine nitrogen abundances and carbon isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. NGC 2506 was found to have a mean [Fe/H]=-0.24±0.05 (standard deviation). Compared with the Sun and other dwarf stars of the Galactic disc, mean abundances in the investigated clump stars suggest that carbon is depleted by about 0.2 dex, nitrogen is overabundant by about 0.3 dex and other chemical elements have abundance ratios close to solar. The C/N and ¹²C/¹³C ratios are lowered to 1.25 ±0.27 and 11±3, respectively.