Abstract
We determine the fundamental parameters of SPB and Beta Cep candidate stars observed by the Kepler satellite mission and estimate the expected types of non-radial pulsators by comparing newly obtained high-resolution spectra with synthetic spectra computed on a grid of stellar parameters assuming LTE and check for NLTE effects for the hottest stars. For comparison, we determine Teff independently from fitting the spectral energy distribution of the stars obtained from the available photometry. We determine Teff, log(g), micro-turbulent velocity, vsin(i), metallicity, and elemental abundance for 14 of the 16 candidate stars, two of the stars are spectroscopic binaries. No significant influence of NLTE effects on the results could be found. For hot stars, we find systematic deviations of the determined effective temperatures from those given in the Kepler Input Catalogue. The deviations are confirmed by the results obtained from ground-based photometry. Five stars show reduced metallicity, two stars are He-strong, one is He-weak, and one is Si-strong. Two of the stars could be Beta Cep/SPB hybrid pulsators, four SPB pulsators, and five more stars are located close to the borders of the SPB instability region.
Highlights
The Kepler satellite delivers light curves of unique accuracy and time coverage, providing unprecedented data for the asteroseismic analysis
We describe a semi-automatic method of spectrum analysis based on the high-resolution spectra of 16 stars (Sect. 2), taken from a list of 34 brighter B-type stars in the Kepler satellite field of view that have been proposed by the Working Groups 3
For the other two stars, surprisingly for Kepler Input Catalogue1 (KIC) 12 258 330 where we assumed LTE, we observe large differences between the values obtained from the two approaches
Summary
The Kepler satellite delivers light curves of unique accuracy and time coverage, providing unprecedented data for the asteroseismic analysis. The identification of non-radial pulsation modes and the asteroseismic modelling, on the other hand, require a classification of the observed stars in terms of Teff, log g, v sin i, and metallicity. These basic stellar parameters cannot be obtained using only Kepler’s single-bandpass photometry. They can be deduced from multi-colour photometry and from spectroscopy and that is why ground-based observations of the Kepler target stars are urgently needed. The surface gravity given in the KIC has an uncertainty of ±0.5 dex, which is much too high for an accurate classification of the stars in terms of non-radial pulsators.
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