The Whole Earth Telescope (WET) project involves over a dozen observatories around the world in coordinated observational campaign to observe white dwarfs. During a given multi-week international campaign, target stars are observed around-the-clock. From these continuous records of photometric variability, many different frequencies of oscillation can be detected. Each is related directly to a given depth, opacity, density, and ionization state in the stellar interior. Detailed analysis of the frequencies observed yields high precision cooling rates, composition and masses that are unachievable by any other means. Analogous to earthquake studies of the Earth's interior, asteroseismology provides one of the few observational verifications of theoretical models of stellar interiors.
Variability in pulsation amplitudes of white dwarfs has been found on all of the timescales studied to date-from hours to years. The basic structure of the star implied by the models remains stable, but additional amplitude modulation appears in the improved observational data, suggesting that current models are incomplete in significant ways. This project will monitor these ongoing changes and look for patterns in the data. Its primary focus is the effort to improve the theoretical models, especially the effects of crystallization, H and He atmosphere layer thickness, and interior C/O abundance.
