This award makes possible a collaboration in astrophysics between Prof. J. Robert Buchler and his group at the University of Florida, and Dr. Peter Wood and his group at the Australian National University. They share an interest in variable stars, particularly in the type referred to as "pulsating Asymptotic Giant Branch (AGB) stars." Their collaboration benefits from sharing of resources and expertise: the Australian collaborator has access to, and is thoroughly familiar with, the MACHO (Massive Compact Halo Objects) astronomical data archive on variable stars, and he has longstanding interest and expertise in the modeling of long-period variables. The American PI has developed unique and specialized computer tools for the analysis of the observational data, and he has longstanding experience with the (nonlinear) numerical hydrodynamical modeling of stellar pulsations.
SCIENTIFIC MERIT
The important groups of irregularly pulsating stars to be studied in this collaboration include the W Virginis type, the RV Tauri type, the Semi-regular variable stars and some of the variable stars in the Mira region. These bright variable stars are playing an increasingly important role in the observational study of star clusters and dwarf galaxies where standard candles such as classical Cepheid stars may be rare. The investigators' 'asteroseismological' goal is to extract unique, quantitative information from the analysis of the observed irregular light curves. A test is also planned of the hypothesis that a single resonant mechanism is at the heart of the irregular pulsations of these stars. Further, the study will shed new light on the uncertain evolutionary status of these stars. New observational data, novel methods of analysis adapted from nonlinear dynamics, and progress in numerical convective hydrocodes lend such a study a timely status.
BROADER IMPACT
Postdoctoral fellows and graduate students on both sides will benefit from the proposed international collaboration. The project also has a broader impact, in that the techniques they have developed are very useful in other research areas as well, ranging from astronomy to nonlinear dynamics to medicine. Two of the PI's codes are being made user-friendly and publicly accessible: TIFRAN, the time-frequency analysis, has medical applications as a diagnostic tool for speech disorders, otolaryngology and neurology among other things, and FLOWRECON, the flow reconstruction from a time-series, has wide applications in nonlinear dynamics research. Under the supervision of the PI, an undergraduate student has started developing a popular audio and video website on variable stars. The teaching of the large undergraduate noncalculus Physics class provides the PI with the opportunity to bring astrophysics, and his own research in particular, to the classroom.
