Astron. J., 146, 143 (2013/December-0)
WIYN open cluster study. LVII. Oxygen abundances of solar-type dwarfs in the Hyades and NGC 752.
MADERAK R.M., DELIYANNIS C.P., KING J.R. and CUMMINGS J.D.
Abstract (from CDS):
Oxygen has been proposed to be a superior tracer, compared to iron, for studying galactic chemical evolution. In the context of improving our understanding of the evolution of Galactic oxygen using open clusters, we present a spectroscopic analysis of oxygen and iron abundances in the 650 Myr old Hyades cluster and in the 1.45 Gyr old cluster NGC 752, using high-dispersion 7774 Å O I triplet region spectra of dwarfs in these clusters acquired with the Hydra MOS on the WIYN 3.5 m telescope. Motivated by recent improvements in analysis of the triplet, we use a strictly differential analysis in solar-type stars to obtain reliable O abundances. Using stars whose radial velocities and spectral cross-correlation analyses are consistent with single-star membership, we report Hyades cluster averages of [O/H] = 0.195±0.010 and [Fe/H] = 0.130 ± 0.009 based on 22 stars, and NGC 752 cluster averages of [O/H] = -0.077 ± 0.02 and [Fe/H] = -0.063±0.013 based on 36 stars (where the errors are σµ; we discuss possible additional systematic errors). These cluster abundance averages are in very good agreement with most previous determinations. Whereas the [O/H] cluster averages utilize only stars found in the "prime" Teff range straddling the solar Teff, the [Fe/H] cluster averages come from stars exhibiting a flat [Fe/H]-Teff relation of over 1000 K for the Hyades and nearly 2000 K for NGC 752. Previous studies of open clusters younger than NGC 752 have reported oxygen triplet over abundances in cool dwarfs, as compared to oxygen abundances of the prime-Teffrange. We report that NGC 752 also shows such overabundances, at a higher level than the Hyades overabundances, and thus contradicts the idea of a decline of such overabundances with increasing age. We discuss evidence for and against correlations of the oxygen overabundances with rotation, X-ray luminosity, chromospheric activity, and metallicity.
open clusters and associations: individual (Hyades, NGC 752) - stars: abundances - stars: activity
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