The chemical compositions and evolutionary status of red giants in the open cluster NGC 752

Abstract

We present detailed chemical compositions of 10 red giant star members of the Galactic (open) cluster NGC 752, derived from high-resolution (R ≈ 60 000), high signal-to-noise (S/N ≥ 140) spectra. We confirmed cluster memberships by measuring the stellar radial velocities, and by deriving model atmosphere parameters (Teff, log g, [Fe/H] and ξt) from equivalent widths of Fe i, Fe ii, Ti i, and Ti ii lines. The metallicity we obtained for NGC 752 ([Fe/H] = −0.02 ± 0.05) is in good agreement with previous studies. We derived abundances of α (Mg, Si, Ca), light odd-Z (Na, Al), Fe-group (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), n-capture (Y, La, Nd, Eu), and p-capture (Li, C, N, O) species for each star. Furthermore, we also derived abundances of the LiCNO p-capture element group and carbon isotopic ratios, using synthetic spectrum analyses of the Li i 6707 Å resonance doublet, the [O i] line at 6300 Å, the CH G-band features near 4311 and 4325 Å, the C2 bandheads at 5160 and 5631 Å, and 12,13CN red system lines in the 7995–8040 Å region. By applying recent isochrones to NGC 752 photometry, and comparing the colour–magnitude diagram information to our Li abundances and 12C/13C ratios, we suggest that the 10 observed red giants can be separated into three first-ascent, six red-clump and one red horizontal branch star.