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Testing Asteroseismic Scalings for Red Giants with Eclipsing Binaries Observed by Kepler
Jean McKeever (New Mexico State University), Patrick Gaulme, Jason Jackiewicz, Meredith Rawls
Given the potential of ensemble asteroseismology for understanding fundamental properties of large numbers of stars, it is critical to determine the accuracy of the scaling relations on which these measurements are based (e.g. Stello et al. 2009, White et al. 2011, Miglio et al. 2013, Huber et al. 2011, Huber et al. 2012, Silva-Aguirre et al. 2012). From several powerful validation techniques, all indications so far show that stellar radius estimates from the asteroseismic scaling relations are accurate within a few percent. Eclipsing binary systems hosting at least one star with detectable solar-like oscillations constitute the most ideal test objects for validating asteroseismic radius and mass inferences. By combining radial-velocity measurements and photometric time series of eclipses, it is possible to determine the masses and radii of each component of a double-lined spectroscopic binary. So far, all published stars known to both display solar-like oscillations and belong to an eclipsing binary are red giants, all having been detected by the Kepler mission (Hekker et al. 2010, Frandsen et al. 2013, Gaulme et al. 2013, 2014, 2016 (submitted), Beck et al. 2014, 2015, Brogaard et al. 2016). Here we report the results of a four-year radial-velocity survey performed with the echelle spectrometer of the Astrophysical Research Consortium's 3.5-m telescope at Apache Point Observatory. We compare the masses and radii of 10 red giants, obtained by combining radial velocities and eclipse photometry with the estimates from asteroseismic scalings. We find that asteroseismic scalings overestimate red-giant radii by about 5% on average and masses by about 15% for stars at various stages of red-giant evolution. While these results are very encouraging in some specific cases, systematic overestimation of mass leads to underestimation of stellar age, which can have important implications for ensemble asteroseismology used for galactic studies.