Critical Tests Of Stellar Evolution Theory

Smithsonian Institution Astrophysical Observatory, Cambridge MA

Investigators

Abstract

The principal investigator will accurately measure the global properties of stars, like their mass, size, brightness, temperature, and composition. He will use these measurements to improve the ability of computer models to predict stellar properties at various stages in their life cycles. Such models are the foundation of our understanding of how our Milky Way Galaxy and its member stars (including our Sun) reached their present state. They also tell us about the timescale for planet formation, which has a significant impact on how well we understand the origin of planets like our own. Despite advances in recent decades, stellar models still show some significant disagreements with observations. The measurements obtained by this project will help to improve stellar physics, and it will offer valuable opportunities to engage students in all aspects of scientific research, providing support for two summer undergraduate students each year. The project will measure the fundamental properties of carefully-selected target stars in eclipsing or astrometric binary systems, which will provide the strongest constraints on theory. The sample includes low-mass stars, which have been shown to often be larger and cooler than predicted by models, for reasons that are still unclear. The main goal is to obtain highly accurate measurements of the absolute masses, radii, effective temperatures, luminosities, chemical composition, and other properties of the components, aiming at relative precisions of 1-2% in the masses and radii. The observational component of the project will include photometric light curves, high-resolution spectra, and long-baseline interferometry. Specific aspects of theory that will be tested include convection (mixing length approximation, overshooting), tidal effects that lead to rotational synchronization and orbital circularization, and the effects of magnetic activity and spots on the absolute stellar properties.