Name/Affiliation: Tiffany D. Pewett (Georgia State University)
Understanding the Wide Main Sequence Through Our Low Mass Neighbors
The RECONS (REsearch Consortium On Nearby Stars, www.recons.org) team has compiled the highest quality astrometric (parallaxes) and photometric (most importantly, VRIJHK) data currently available for over 3000 stars within 25 parsecs. This allows us to create an exquisite map of the main sequence in the H-R Diagram from A stars through M stars. Careful analysis of the H-R Diagram reveals a curious thing --- the main sequence is widest, by up to 2.5 full magnitudes in Mv, in the region of low mass K and M dwarf stars. This corresponds to a factor of almost 10 in luminosity among stars of the same temperature. A detailed understanding of the causes of this width still remains elusive and complex. Given that temperature and radius determine the observed luminosity of a star, stars with identical temperatures must have radii differing by up to a factor of three to account for the width of the main sequence. In order to determine the underlying causes of the different radii, we have embarked on a project to measure the properties of a large sample of the nearest low mass stars. So far this includes investigations of variability, radii, surface gravities, and metallicities. We compare the main sequence stars to nearby young stars and cool subdwarfs with similar colors to map the complex interplay of these many factors. Here we present initial results from the photometric variability data and recently obtained spectra. This effort is supported by the NSF through grants AST-0908402 and AST-1109445, and via observations made possible by the SMARTS Consortium.