In this project, Dr. Hebb and her collaborators will conduct a three-part study of the fundamental properties of low-mass stars. In the last decade, it has become apparent to the stellar community that theoretical models of the masses and radii of unevolved low-mass stars differ significantly from observations. In this study, Dr. Hebb will determine the chemical abundances of certain stars where the masses, radii, and temperatures are accurately known, explore the effect of magnetically-induced activity on the determinations of luminosity and radius, and obtain critical data on very young systems to test models of the phases leading up to full hydrogen fusion.
The project is expected to have a broad scientific impact because fundamental stellar data can be used in a variety of applications, including the determination of exoplanet masses and the characterization of the star formation process. The research team will also continue their work with students at Vanderbilt and at Fisk College.
We have conducted a long-term program to discover and study "benchmark grade" eclipsing binary stars with which to test stellar evolution models of newly formed stars. We have produced a major review, published in New Astronomy Reviews, analyzing the performance of all current stellar evolution theories against the precise measurements provided by the large number of eclipsing binary star systems that we have discovered. Interestingly, we find that the stellar systems that appear discrepant relative to the theoretical models are those that possess a third ("tertiary") star in the system in addition to the eclipsing pair. Evidently, and importantly, triplet stars engage in physics that corrupts the expected properties of the central twins. We have also analyzed the detailed chemical abundances ("metallicities") of binary stars that host planets, with the important and interesting finding that trends in the chemical compositions of these stars can be explained by past episodes of ingestion by the stars of rocky Earth-like material. Evidently, the formation of solar systems around Sun-like stars may often involve a "survival of the fittest" in which many if not most forming planets are eaten by their parent stars. We have also determined an empirical relationship between the magnetism of a star and the degree to which its radius is "bloated", which is important for ascertaining the true physical properties of magnetic stars and of the planets that may orbit them. Finally, we have advanced the national effort to broaden participation of underrepresented minorities in astronomy through the Fisk-Vanderbilt Masters-to-PhD Bridge Program, which has enabled PhD dissertations of underrepresented minoritiy students leading the discoveries listed above and others.
