The chemical compositions and evolutionary status of red giants in the open cluster NGC 6940
Makaleler > Tam Makale · 2016
Yazarlar: G. Bocek TOPCU, Melike AFŞAR, C. SNEDEN
Monthly Notices of the Royal Astronomical Society, SCI Expanded İndekslerine Giren Dergi, Uluslararası, Wos, 2016, cilt 463, ss 580-597
Özet
We present the high-resolution (R ≈ 60 000), high signal-to-noise ratio (S/N ≃ 120) spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. We applied Yonsei–Yale isochrones to the colour–magnitude diagram, which suggested an age of 1.1 Gyr for the cluster with a turn-off mass of 2 M⊙. Atmospheric parameters (Teff, log g, [Fe/H], and ξt) were determined via equivalent widths of Fe i, Fe ii, Ti i, and Ti ii lines. Calculated mean metallicity of the cluster is 〈[Fe/H]〉 = 0.04 ± 0.02. We derived abundances of α (Mg, Si, Ca), Fe-group (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and n-capture (Y, La, Nd, Eu) elements to be about solar. Light odd-Z elements Na and Al are slightly enhanced in MMU 108 and MMU 152 by ∼0.34 and ∼0.16 dex, respectively. Abundances of light elements Li, C, N, O, and 12C/13C ratios were derived from spectrum syntheses of the Li i resonance doublet at 6707 Å, [O i] line at 6300 Å, C2 Swan bandheads at 5164 and 5635 Å, and strong 12,13CN system lines in the 7995–8040 Å region. Most carbon isotopic ratios are similar to those found in other solar-metallicity giants, but MMU 152 has an unusual value of 12C/13C = 6. Evaluation of the LiCNO abundances and 12C/13C ratios along with the present theoretical models suggests that all the red giants in our sample are core-helium-burning clump stars.