Accurate fundamental parameters and detailed abundance patterns from spectroscopy of 93 solar-type Kepler targets
Kawaler, S. D.; Christensen-Dalsgaard, J.; García, R. A.; Chaplin, W. J.; Uytterhoeven, K.; Catala, C.; Stello, D.; Kjeldsen, H.; Handberg, R.; Mosser, B.; Hekker, S.; Elsworth, Y.; Appourchaux, T.; Mathur, S.; Smalley, B.; Huber, D.; Bruntt, H.; Bedding, T. R.; Molenda-Żakowicz, J.; Metcalfe, T. S.; Quintana, E. V.; Verner, G. A.; Régulo, C.; Roxburgh, I. W.; Gazzano, J. -C.; Basu, S.; Campante, T. L.; Karoff, C.; Quirion, P. -O.; Thygesen, A. O.; Morris, R. L.; Sanderfer, D. T.
Denmark, France, United States, United Kingdom, Australia, Poland, Spain, Netherlands, Portugal, Canada
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 accuracy on the log g parameter is better than 0.03 dex and is held fixed in the analysis. We compare our Teff determination with a recent colour calibration of VT-KS [TYCHO V magnitude minus Two Micron All Sky Survey (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 of metals, 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.