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Verifying Asteroseismically Determined Parameters of Kepler Stars Using Hipparcos Parallaxes: Self-consistent Stellar Properties and Distances
Accurately determining the properties of stars is of prime importancefor characterizing stellar populations in our Galaxy. The field ofasteroseismology has been thought to be particularly successful in suchan endeavor for stars in different evolutionary stages. However, tofully exploit its potential, robust methods for estimating stellarparameters are required and independent verification of the results ismandatory. With this purpose, we present a new technique to obtainstellar properties by coupling asteroseismic analysis with the InfraRedFlux Method. By using two global seismic observables and multi-bandphotometry, the technique allows us to obtain masses, radii, effectivetemperatures, bolometric fluxes, and hence distances for field stars ina self-consistent manner. We apply our method to 22 solar-likeoscillators in the Kepler short-cadence sample, that have accurateHipparcos parallaxes. Our distance determinations agree to better than5%, while measurements of spectroscopic effective temperatures andinterferometric radii also validate our results. We briefly discuss thepotential of our technique for stellar population analysis and models ofGalactic Chemical Evolution.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Spectroscopic Study of Candidates for Kepler Asteroseismic Targets - Solar-Like Stars
We report spectroscopic observations of 23 candidates for Keplerasteroseismic targets and 10 other stars in the Kepler field. For allthese stars, we derive the radial velocities, effective temperature,surface gravity, metallicity, the projected rotational velocity, andestimate the MK type. HIP 97513 and HIP 92132 are classified assuspected new single-lined spectroscopic binaries. For 28 stars, theradial velocity is measured for the first time.
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