Meredith L. Rawls

and 9 more

We combine _Kepler_ photometry with ground-based spectra to present a comprehensive dynamical model of the double red giant eclipsing binary KIC 9246715. While the two stars are very similar in mass ($M_1 = 2.171 \ M_{\odot}$, $M_2 = 2.149 \ M_{\odot}$) and radius ($R_1 = 8.37 \ R_{\odot}$, $R_2 = 8.30 \ R_{\odot}$), an asteroseismic analysis finds one main set of solar-like oscillations with unusually low-amplitude, wide modes. A second set of oscillations from the other star may exist, but this marginal detection is extremely faint. Because the two stars are nearly twins, KIC 9246715 is a difficult target for a precise test of the asteroseismic scaling relations, which yield M = 2.17 ± 0.14 M⊙ and R = 8.26 ± 0.18 R⊙. Both stars are consistent with the inferred asteroseismic properties, but we suspect the main oscillator is Star 2 because it is less active than Star 1. We find evidence for stellar activity and modest tidal forces acting over the 171-day eccentric orbit, which are likely responsible for the essential lack of solar-like oscillations in one star and weak oscillations in the other. Mixed modes indicate the main oscillating star is on the secondary red clump (a core-He-burning star), and stellar evolution modeling supports this with a coeval history for a pair of red clump stars. This system is a useful case study and paves the way for a detailed analysis of more red giants in eclipsing binaries, an important benchmark for asteroseismology.
INTRODUCTION Stars are the fundamental observable in astrophysics. For this reason, much has been done to advance our understanding of stellar properties. Such work has many applications: beyond a simple desire to better understand how stars form, live, and evolve, stars are critical to understanding everything from our own Sun to the structure of galaxies. At this particularly exciting time, as extrasolar planets turn up everywhere we look, it is important to realize that our characterization of these planets is only as good as our understanding of their host stars. For this reason alone, any technique that allows us to characterize large numbers of stars both quickly and accurately is important. Recently, asteroseismology has emerged as such a tool. Many stars with convective envelopes exhibit solar-like oscillations, which are a powerful way to probe stellar interiors. The recent _Kepler_ mission was particularly well-suited to detect these, because it observed the same targets for a long period of time with a regular cadence. In particular, red giant stars with solar-like oscillations pulsate more slowly than our Sun due to their large size, and therefore appear in _Kepler_ long-cadence (∼30 min) data. Observing solar-like oscillations in red giants can tell us many things with relative ease: density, surface gravity, mass, radius, and even evolutionary stage. However, it is not always clear why some red giants willingly broadcast their inner secrets while others do not oscillate, or oscillate with lower amplitudes than we might expect. Given the power of asteroseismology coupled with our limited understanding of why it works when it does, it is imperative to study solar-like oscillators in environments that are observationally accessible using techniques independent of asteroseismology. One such accessible environment is eclipsing binary stars. and identified some 20 red giants in eclipsing binaries (hereafter RG/EBs) in the _Kepler_ field, most of which show solar-like oscillations but some of which do not. They also identified several triple systems consisting of two main sequence stars in an eclipsing binary that show transit timing variations due to the orbit of an oscillating red giant. The purpose of this work is to use the many tools available for modeling eclipsing binaries to piece together a “life story” of several RG/EBs, thereby giving more context to the results from asteroseismology and enabling us to understand what makes evolved stars oscillate in some situations but not others. In this thesis proposal, we first review relevant literature in Section [background]. We then present the main science questions to be addressed in Section [questions]. Sections [data] and [method] outline the proposed project, while Section [results] describes anticipated results. Finally, we summarize the project and conclude in Section [conclusion], and present the proposed timeline in Section [timeline].