Spectral analysis of Kepler SPB andβ Cephei candidate stars

Abstract

Context. For an asteroseismic modeling, the analysis of the high-accuracy light curves delivered by the Kepler satellite mission needs support by ground-based multi-colour and spectroscopic observations. Aims. We determine the fundamental parameters of SPB and β Cep candidate stars observed by the Kepler satellite mission and estimate the expected types of non-radial pulsators. Methods. We compare 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 T eff independently from fitting the spectral energy distribution of the stars obtained from the available photometry. Results. We determine T eff , log g, micro-turbulent velocity, v sin 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 β Cep/SPB hybrid pulsators, four SPB pulsators, and five more stars are located close to the borders of the SPB instability region.

Denoising spectroscopic data by means of the improved least-squares deconvolution method

“…Obviously, all five atmospheric parameters are in perfect agreement with the values reported by Lehmann et al (2011), which in turn agree very well with several recent findings for this star (see, e.g., Table 3 in Lehmann et al 2011). It is worth noting that the errors in both T eff and log g are slightly higher than those estimated by Lehmann et al (2011). This result also seems to be reasonable as in our analysis we rely purely on metal lines, without using Balmer profiles which are a good indicator of the effective temperature and surface gravity in this temperature range.…”

“…We used the obtained model spectrum (free of Balmer and helium lines) to estimate the fundamental parameters of the star by means of our GSSP code. of Vega that we obtained with those found by Lehmann et al (2011) using the same atmosphere models and spectrum synthesis codes as we did. Obviously, all five atmospheric parameters are in perfect agreement with the values reported by Lehmann et al (2011), which in turn agree very well with several recent findings for this star (see, e.g., Table 3 in Lehmann et al 2011).…”

“…of Vega that we obtained with those found by Lehmann et al (2011) using the same atmosphere models and spectrum synthesis codes as we did. Obviously, all five atmospheric parameters are in perfect agreement with the values reported by Lehmann et al (2011), which in turn agree very well with several recent findings for this star (see, e.g., Table 3 in Lehmann et al 2011). It is worth noting that the errors in both T eff and log g are slightly higher than those estimated by Lehmann et al (2011).…”

“…We then use the final list of the line strengths and the LSD profile to compute a model spectrum and analyse it to determine the fundamental parameters which are then compared to the originally assumed ones. To estimate the fundamental parameters we rely on the spectral synthesis method as implemented in the GSSP (grid search in stellar parameters) code (Tkachenko et al 2012a;Lehmann et al 2011). The code finds the optimum values of T eff , log g, ξ, [M/H], and v sin i from the minimum in χ 2 obtained from a comparison of the observed spectrum with the synthetic ones computed from all possible combinations of the above-mentioned parameters.…”

V342 Andromedae B is an eccentric-orbit eclipsing binary

“…9). For our analysis, we used the GSSP program (see Lehmann et al 2011 andTkachenko et al 2012 for a description of the method). We extended the method to a simultaneous fit of two components in a composite spectrum by two synthetic spectra calculated on two grids in stellar parameters.…”