Atmospheric parameters of red giants in the Kepler field

Abstract

Accurate fundamental parameters of stars are mandatory for the asteroseismic investigation of the Kepler mission to succeed. We will determine the atmospheric parameters for a sample of 6 well-studied bright K giants to confirm that our method produces reliable results. We then apply the same method to 14 K giants that are targets for the Kepler mission. We have used high-resolution, high signal-to-noise spectra from the FIES spectrograph on the Nordic Optical Telescope. We used the iterative spectral synthesis method VWA to derive the fundamental parameters from carefully selected high-quality iron lines and pressure-sensitive Calcium lines. We find good agreement with parameters from the literature for the 6 bright giants. We compared the spectroscopic values with parameters based on photometric indices in the Kepler Input Catalogue (KIC). We identify serious problems with the KIC values for [Fe/H] and find a large RMS scatter of 0.5 dex. The log g values in KIC agree reasonably well with the spectroscopic values with a scatter of 0.25 dex, when excluding two low-metallicity giants. The Teffs from VWA and KIC agree well with a scatter of about 85 K. We also find good agreement with log g and Teff derived from asteroseismic analyses for seven Kepler giant targets. We have determined accurate fundamental parameters of 14 giants using spectroscopic data. The large discrepancies between photometric and spectroscopic values of [Fe/H] emphasize the need for further detailed spectroscopic follow-up of the Kepler targets. This is mandatory to be able to produce reliable constraints for detailed asteroseismic analyses and for the interpretation of possible exo-planet candidates found around giant stars.

6 pages, 4 figures, accepted by A&A

References in corpus (7)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Asteroseismology of red giants from the first four months of Kepler data: Fundamental parameters
• A spectroscopic study of southern (candidate) gamma Doradus stars. II. Detailed abundance analysis and fundamental parameters
• Multisite campaign on the open cluster M67. II. Evidence for solar-like oscillations in red giant stars
• Solar-like oscillations in the metal-poor subgiant nu Indi: constraining the mass and age using asteroseismology
• Solar-like oscillations in a metal-poor globular cluster with the HST
• A search for solar-like oscillations in K giants in the globular cluster M4

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