Atmospheric parameters of 82 red giants in the Kepler field

TL;DR

This study provides precise atmospheric parameters and element abundances for 82 red giants in the Kepler field, highlighting discrepancies with catalog data and supporting improved asteroseismic analysis.

Contribution

It offers detailed spectroscopic measurements of red giants, revealing significant differences from catalog parameters and emphasizing the importance of spectroscopic follow-up.

Findings

Discrepancies in log g and [Fe/H] compared to Kepler Input Catalogue

Good agreement between spectroscopic and asteroseismic log g

Potential metallicity effects on stellar oscillations

Abstract

Context: Accurate fundamental parameters of stars are essential for the asteroseismic analysis of data from the NASA Kepler mission. Aims: We aim at determining accurate atmospheric parameters and the abundance pattern for a sample of 82 red giants that are targets for the Kepler mission. Methods: We have used high-resolution, high signal-to-noise spectra from three different spectrographs. We used the iterative spectral synthesis method VWA to derive the fundamental parameters from carefully selected high-quality iron lines. After determination of the fundamental parameters, abundances of 13 elements were measured using equivalent widths of the spectral lines. Results: We identify discrepancies in log g and [Fe/H], compared to the parameters based on photometric indices in the Kepler Input Catalogue (larger than 2.0 dex for log g and [Fe/H] for individual stars). The Teff found from spectroscopy and photometry shows good agreement within the uncertainties. We find good agreement between the spectroscopic log g and the log g derived from asteroseismology. Also, we see indications of a potential metallicity effect on the stellar oscillations. Conclusions: We have determined the fundamental parameters and element abundances of 82 red giants. The large discrepancies between the spectroscopic log g and [Fe/H] and values in the Kepler Input Catalogue emphasize the need for further detailed spectroscopic follow-up of the Kepler targets in order to produce reliable results from the asteroseismic analysis.