In this project, Drs. Oswalt and Holberg will undertake a study of widely separated "fragile binary stars" that contain normal lower mass main sequence stars with distant noninteracting white dwarf companions. As stars evolve to the white dwarf stage, most lose well over half their original mass. This initial-to-final mass relation is one of the weakest links in our understanding of stellar evolution and how matter is recycled into the interstellar medium. It is also of special importance to a number of different areas in astrophysics such as age and distance determinations of globular clusters, studying the chemical evolution of galaxies, and also for understanding the history of star formation as recorded by the Galaxy's remnant white dwarfs.
For several decades it has been known that stellar chromospheric activity declines with age in Solar-type stars. Dr. Oswalt and collaborators have recently shown evidence that this trend is valid to nearly the expected age of the Galactic disk. Other work has demonstrated stellar ages can be determined by isochrone fitting in color magnitude diagrams or via stellar rotation rates obtained from simple photometric observations. These techniques will be applied here, where appropriate, to determine the ages of a sample of wide separation binaries with white dwarfs. The ages of the white dwarfs themselves, which span the entire history of the Solar neighborhood, can be determined from their observed temperatures. And by subtracting the ages of the white dwarf companions from the total age of the binary yields its progenitor main sequence lifetime and initial mass. In this way, they will empirically calibrate the initial-to-final mass relation for white dwarf stars to at least the age of the Sun.
The Florida Tech Department of Physics & Space Sciences is home to one of the largest astronomy-related undergraduate programs in the U.S. In autumn 2007 it enrolled 142 majors. About half are women and/or minorities. Undergraduates will be involved in all aspects of the project, from data acquisition with the Southeastern Association for Research in Astronomy (SARA) 0.9m and Florida Tech 0.8m telescopes, to presenting our results to the scientific community. Two graduate students will also conduct dissertation projects directly related to this project. A postdoctoral research fellow will work closely with Drs. Oswalt and Holberg and the students to derive an independent age determination for each of the wide binaries via the isochrone technique. Co-PI Holberg will lead the effort to incorporate the physical data on the white dwarf components of wide binaries obtained by this project into the University of Arizona White Dwarf Database, which is a widely used by the international astronomical community and general public. Results of this project will be brought into astronomy courses and to the public via the Florida Institute of Technology Observatory Astronomy/Astrophysics Lecture Series, AAS Shapley Lectures, and other media. It is also anticipated that K-12 students will participate in the data acquisition phase of the project via the Global Hands-On Universe project.
