The Chemical Compositions and Evolutionary Status of Red Giants in the Open Cluster NGC 752

TL;DR

This study provides detailed chemical compositions of 10 red giants in NGC 752, confirming cluster membership and analyzing their evolutionary status through high-resolution spectroscopy and comparison with stellar models.

Contribution

It offers the first comprehensive chemical abundance analysis of red giants in NGC 752, including Li, CNO, and isotopic ratios, and classifies their evolutionary stages.

Findings

Cluster metallicity [Fe/H] = -0.02 ± 0.05 matches previous studies.

Red giants are classified into first-ascent, red-clump, and red horizontal branch stars.

Detailed elemental abundances for multiple species are provided for each star.

Abstract

We present detailed chemical compositions of 10 red giant star members of the Galactic (open) cluster NGC 752, derived from high-resolution (R $\approx$ 60,000), high signal-to-noise ($S/N$ $\geq$ 140) spectra. We confirmed cluster memberships by measuring the stellar radial velocities, and by deriving model atmosphere parameters ($T_{eff}$, logg, [Fe/H] and $\xi_{t}$) from equivalent widths of Fe I, Fe II, Ti I, and Ti II lines. The metallicity we obtained for NGC 752 ([Fe/H]=$-$0.02$\pm$0.05) is in good agreement with previous studies. We derived abundances of $\alpha$ (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~\AA\ resonance doublet, the [O I] line at 6300~\AA, the CH G-band features near 4311 and 4325 \AA, the C$_{2}$ bandheads at 5160 and 5631 \AA, and $^{12,13}$CN red system lines in the 7995$-$8040~\AA\ region. By applying recent isochrones to NGC~752 photometry, and comparing the color-magnitude diagram information to our Li abundances and \ciso\ 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.