Collaborative Research: A uniform sample of Kepler eclipsing binaries as benchmark stars to constrain stellar models and evolution at the bottom of the main sequence

This research program will improve our understanding of low-mass stars (those with less than 80% of the Sun's mass). The team will obtain extremely precise measurements of the masses and radii of nearly 200 eclipsing binary stars. These measurements will drive improvements in theoretical models of stars. These models are used across a wide range of astrophysical disciplines, and they are particularly important for characterizing the tremendous number of exoplanets that astronomers are discovering. Accurate models of stars are needed to evaluate the habitability of Earth mass planets, and the results from this program will be particularly timely as the next generation of exoplanet searches begins explicitly targeting low-mass stars. This Penn State and Villanova collaboration involves undergraduate, graduate, and postdoctoral researchers in all facets of the research, and members of both teams actively participate in public outreach events.

The primary objective of this program is to measure the mass and radius of binary stars with precision better than 3%, while also characterizing the stars' compositions. This measurement precision is necessary to address well recognized discrepancies for low-mass stars of 5-15% between predictions of current models and the handful of existing measurements. These measurements are achieved through the combination of ultra-precise photometry from NASA's Kepler observatory and extensive high-resolution ground-based spectroscopy from near-infrared and visible wavelength spectrographs (APOGEE, HYDRA, HRS) that have been collected by the team. Data are analyzed with cutting-edge algorithms for light-curve modelling (PHOEBE), multi-dimensional radial velocity measurements (TODCOR/TRICOR), and Markov Chain Monte Carlo techniques for assessing robust and repeatable parameters and parameter uncertainties. Results from this program will more than double the number of low-mass stars with both precision mass and radius measurements, and with spectroscopically determined compositions.