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Register a new userBayesian Asteroseismology of 23 Solar-Like Kepler Targets
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Added by
Michael Gruberbauer
Publication date
2013
fields
Physics
and research's language is
English
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We study 23 previously published Kepler targets to perform a consistent grid-based Bayesian asteroseismic analysis and compare our results to those obtained via the Asteroseismic Modelling Portal (AMP). We find differences in the derived stellar parameters of many targets and their uncertainties. While some of these differences can be attributed to systematic effects between stellar evolutionary models, we show that the different methodologies deliver incompatible uncertainties for some parameters. Using non-adiabatic models and our capability to measure surface effects, we also investigate the dependency of these surface effects on the stellar parameters. Our results suggest a dependence of the magnitude of the surface effect on the mixing length parameter which also, but only minimally, affects the determination of stellar parameters. While some stars in our sample show no surface effect at all, the most significant surface effects are found for stars that are close to the Suns position in the HR diagram.
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We use various method to extract surface rotation periods of Kepler targets exhibiting solar-like oscillations and compare their results.
We comment on the potential for continuing asteroseismology of solar-type and red-giant stars in a 2-wheel Kepler Mission. Our main conclusion is that by targeting stars in the ecliptic it should be possible to perform high-quality asteroseismology, as long as favorable scenarios for 2-wheel pointing performance are met. Targeting the ecliptic would potentially facilitate unique science that was not possible in the nominal Mission, notably from the study of clusters that are significantly brighter than those in the Kepler field. Our conclusions are based on predictions of 2-wheel observations made by a space photometry simulator, with information provided by the Kepler Project used as input to describe the degraded pointing scenarios. We find that elevated levels of frequency-dependent noise, consistent with the above scenarios, would have a significant negative impact on our ability to continue asteroseismic studies of solar-like oscillators in the Kepler field. However, the situation may be much more optimistic for observations in the ecliptic, provided that pointing resets of the spacecraft during regular desaturations of the two functioning reaction wheels are accurate at the < 1 arcsec level. This would make it possible to apply a post-hoc analysis that would recover most of the lost photometric precision. Without this post-hoc correction---and the accurate re-pointing it requires---the performance would probably be as poor as in the Kepler-field case. Critical to our conclusions for both fields is the assumed level of pointing noise (in the short-term jitter and the longer-term drift). We suggest that further tests will be needed to clarify our results once more detail and data on the expected pointing performance becomes available, and we offer our assistance in this work.
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.
We report on the first asteroseismic analysis of solar-type stars observed by Kepler. Observations of three G-type stars, made at one-minute cadence during the first 33.5d of science operations, reveal high signal-to-noise solar-like oscillation spectra in all three stars: About 20 modes of oscillation can clearly be distinguished in each star. We discuss the appearance of the oscillation spectra, including the presence of a possible signature of faculae, and the presence of mixed modes in one of the three stars.
Observations from the Kepler satellite were recently published for three bright G-type stars, which were monitored during the first 33.5d of science operations. One of these stars, KIC 11026764, exhibits a characteristic pattern of oscillation frequencies suggesting that the star has evolved significantly. We have derived initial estimates of the properties of KIC 11026764 from the oscillation frequencies observed by Kepler, combined with ground-based spectroscopic data. We present preliminary results from detailed modeling of this star, employing a variety of independent codes and analyses that attempt to match the asteroseismic and spectroscopic constraints simultaneously.
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