Accurate fundamental parameters and detailed abundance patterns from spectroscopy of 93 solar-type Kepler targets

H. Bruntt, S. Basu, B. Smalley, W. J. Chaplin, G. A. Verner, T. R. Bedding, C. Catala, J.-C. Gazzano, J. Molenda-Żakowicz, A. O. Thygesen, K. Uytterhoeven, S. Hekker, D. Huber, C. Karoff, S. Mathur, B. Mosser, T. Appourchaux, T. L. Campante, Y. Elsworth, R. A. García, R. Handberg, T. S. Metcalfe, P.-O. Quirion, C. Régulo, I. W. Roxburgh, D. Stello, J. Christensen-Dalsgaard, S. D. Kawaler, H. Kjeldsen, R. L. Morris, E. V. Quintana, D. T. Sanderfer

Abstract
We present a detailed spectroscopic study of 93 solar-type stars that are targets of the NASA/Kepler mission and provide detailed chemical composition of each target. We find that the overall metallicity is well-represented by Fe lines. Relative abundances of light elements (CNO) and α elements are generally higher for low-metallicity stars. Our spectroscopic analysis benefits from the accurately measured surface gravity from the asteroseismic analysis of the Kepler light curves. The log g parameter is known to better than 0.03 dex and is held fixed in the analysis. We compare our T_eff determinationwith a recent colour calibration of V_T-K_S (TYCHO V magnitude minus 2MASS KS magnitude) and find very good agreement and a scatter of only 80 K, showing that for other nearby Kepler targets this index can be used. The asteroseismic log g values agree very well with the classical determination using Fe _I-Fe _II balance, although we find a small systematic offset of 0.08 dex (asteroseismic log g values are lower). The abundance patterns ofmetals, α elements, and the light elements (CNO) show that a simple scaling by [Fe/H] is adequate to represent the metallicity of the stars, except for the stars with metallicity below -0.3, where α-enhancement becomes important. However, this is only important for a very small fraction of the Kepler sample. We therefore recommend that a simple scaling with [Fe/H] be employed in the asteroseismic analyses of large ensembles of solar-type stars.

Keywords
stars: abundances – stars: atmospheres – stars: fundamental parameters – stars: solar-type

Notes
Based on observations obtained at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii.
Based on observations with the 2-m Telescope Bernard Lyot funded by the CNRS Institut National des Sciences de l’Univers.

Monthly Notices of the Royal Astronomical Society
Volume 423, Page 122
June 2012

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