Meredith L. Rawls edited Introduction.tex  over 8 years ago

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Mass and radius are often-elusive stellar properties that are critical to understanding a star's past, present, and future. Eclipsing binaries are the only astrophysical laboratories that allow for a direct measurement of these and other fundamental physical parameters. Recently, however, observing solar-like oscillations in stars with convective envelopes has opened a window to stellar interiors and provided a new way to measure global stellar properties. A pair of asteroseismic scaling relations use the Sun as a benchmark and an empirical connection between these oscillations and a star's effective temperature to yield mass and radius \citep{kje95,hub10,mos13}.  While both the mass and radius scaling relations are useful, it is important to test their validity. Recent work has investigated the radius relation by comparing the asteroseismic large-frequency separation $\Delta \nu$ and stellar radius between models and simulated data \citep[e.g.][]{ste09,whi11,mig13}, and by comparing asteroseismic radii with independent radius measurements such as interferometry or binary star modeling \citep[e.g.][]{hub11,hub12,sil12}. All of these find that radius estimates from asteroseismology are precise within a few percent, with greater scatter for red giants than main sequence stars. The mass scaling relation remains relatively untested. Most studies test the $\Delta\nu$ scaling with average stellar density and not the scaling of $\nu_{\rm{max}}$ (the asteroseismic frequency of maximum oscillation power) with stellar surface gravity, because the latter has a less-secure theoretical basis. basis \revise{\citep{bel11}}.  It is not yet possible to reliably predict oscillation mode amplitudes as a function of frequency \citep{chr12}. One study by \citet{fra13} did test both scaling laws with the red giant eclipsing binary KIC 8410637. They found good agreement between Keplerian and asteroseismic mass and radius, but a more recent analysis from \citet{hub14} indicates that the asteroseismic density of KIC 8410637 is underestimated by $\sim$7\,\% (1.8~$\sigma$, accounting for the density uncertainties), which results in an overestimate of the radius by $\sim$9\,\% (2.7~$\sigma$) and mass by $\sim$17\,\% (1.9~$\sigma$). Additional benchmarks for the asteroseismic scaling relations are clearly needed. Evolved red giants are straightforward to characterize through pressure-mode solar-like oscillations in their convective zones, and red giant asteroseismology is quickly becoming an important tool to study stellar populations throughout the Milky Way \citep[for a review of this topic, see][]{cha13}. Compared to main-sequence stars, red giants oscillate with larger amplitudes and longer periods---several hours to days instead of minutes. Oscillations appear as spikes in the amplitude spectrum of a light curve that is sampled both frequently enough and for a sufficiently long duration. Therefore, observations from the \emph{Kepler} space telescope taken every 29.4 minutes (long-cadence) over many 90-day quarters are ideal for asteroseismic studies of red giant stars.