6 research outputs found
Accurate fundamental parameters and detailed abundance patterns from spectroscopy of 93 solar-type Kepler targets
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 alpha-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 Teff determination with a
recent colour calibration of V-K (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 Fe1-Fe2 balance,
although we find a small systematic offset of 0.08 dex (asteroseismic log g
values are lower). The abundance patterns of metals, alpha 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 alpha-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.Comment: MNRAS, in press, 12 page
Asteroseismic diagrams from a survey of solar-like oscillations with Kepler
Photometric observations made by the NASA Kepler Mission have led to a
dramatic increase in the number of main-sequence and subgiant stars with
detected solar-like oscillations. We present an ensemble asteroseismic analysis
of 76 solar-type stars. Using frequencies determined from the Kepler
time-series photometry, we have measured three asteroseismic parameters that
characterize the oscillations: the large frequency separation (\Delta \nu), the
small frequency separation between modes of l=0 and l=2 (\delta \nu_02), and
the dimensionless offset (\epsilon). These measurements allow us to construct
asteroseismic diagrams, namely the so-called C-D diagram of \delta \nu_02
versus \Delta \nu, and the recently re-introduced {\epsilon} diagram. We
compare the Kepler results with previously observed solar-type stars and with
theoretical models. The positions of stars in these diagrams places constraints
on their masses and ages. Additionally, we confirm the observational
relationship between {\epsilon} and T_eff that allows for the unambiguous
determination of radial order and should help resolve the problem of mode
identification in F stars.Comment: 6 pages, 5 figures, accepted for publication in The Astrophysical
Journal Letter