The Gaia-ESO Survey: CNO abundances in the open clusters Trumpler 20, NGC 4815, and NGC 6705

Abstract

Aim of this work is to determine C, N, and O abundances in stars of Galactic open clusters of the Gaia-ESO survey and to compare the observed abundances with those predicted by current stellar and Galactic evolution models. In this pilot paper, we investigate the first three intermediate-age open clusters. High-resolution spectra, observed with the FLAMES-UVES spectrograph on the ESO VLT telescope, were analysed using a differential model atmosphere method. Abundances of carbon were derived using the C2 band heads at 5135 and 5635.5 Å. The wavelength interval 6470- 6490 Å, with CN features, was analysed to determine nitrogen abundances. Oxygen abundances were determined from the [O i] line at 6300 Å. The mean values of the elemental abundances in Trumpler 20 as determined from 42 stars are: [Fe/H] = 0.10 +- 0.08 (s.d.), [C/H] = -0.10 +- 0.07, [N/H] = 0.50 +- 0.07, and consequently C/N = 0.98 +- 0.12. We measure from five giants in NGC 4815: [Fe/H] = -0.01 +- 0.04, [C/H] = -0.17 +- 0.08, [N/H] = 0.53 +- 0.07, [O/H] = 0.12 +- 0.09, and C/N = 0.79 +- 0.08. We obtain from 27 giants in NGC 6705: [Fe/H] = 0.0 +- 0.05, [C/H] = -0.08 +- 0.06, [N/H] = 0.61 +- 0.07, [O/H] = 0.13 +- 0.05, and C/N = 0.83 +- 0.19. The C/N ratios of stars in the investigated open clusters were compared with the ratios predicted by stellar evolutionary models. For the corresponding stellar turn-off masses from 1.9 to 3.3 solar masses, the observed C/N ratio values are very close to the predictions of standard first dredge-up models as well as to models of thermohaline extra-mixing. The average [O/H] abundance ratios of NGC 4815 and NGC 6705 are compared with the predictions of two Galactic chemical evolution models. The data are consistent with the evolution at the solar radius within the errors.

13 pages, 11 figures, accepted for publication in Astronomy & Astrophysics, 2014

References in corpus (16)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• Deep Mixing of He-3: Reconciling Big Bang and Stellar Nucleosynthesis
• Gaia-ESO Survey: The analysis of high-resolution UVES spectra of FGK-type stars
• The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters
• Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
• Old open clusters in the outer Galactic disk
• Open clusters as key tracers of Galactic chemical evolution. III. Element abundances in Berkeley 20, Berkeley 29, Collinder 261, and Melotte 66
• The Gaia-ESO Survey: processing of the FLAMES-UVES spectra
• The Gaia-ESO Survey: Stellar content and elemental abundances in the massive cluster NGC 6705
• High resolution infrared spectroscopy of the old open cluster NGC6791
• MHD and deep mixing in evolved stars. 1. 2D and 3D analytical models for the AGB
• The Gaia-ESO Survey: Properties of the intermediate age open cluster NGC 4815
• C, N, O abundances and carbon isotope ratios in evolved stars of the open clusters Collinder 261 and NGC 6253
• Red clump stars of the Milky Way - laboratories of extra-mixing

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