The Life Cycles of Interacting Binary Stars

Pennsylvania State Univ University Park, University Park PA

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). In this project, Dr. Mercedes Richards of the Pennsylvania State University will use spectroscopic analysis, synthetic spectra, tomography, and hydrodynamic simulations to study the early stages of the life cycle of interacting binary stars. The evolutionary sequence for close binaries begins with the formation of two detached stars and ends with evolved systems containing at least one compact object (e.g., novae, supernovae, X-ray binaries, binary pulsars). The transition from the early to late stages depends on the initial mass transfer rate, which is influenced by the structure of the star when it fills its Roche surface, the degree to which orbital angular momentum and system mass are assumed to be conserved, and the response of the companion star to the accretion of gas. Binary evolution models require knowledge of this initial mass loss rate since the donor will lose gas at this rate until the initial mass ratio has been reversed. Dr. Richards will use direct measurements of the gas stream and other accretion structures to determine reliable estimates of the mass transfer rate, gas densities, and gas temperatures for binaries in the slow mass transfer phase. She will apply a new approach to isolate the separate spectroscopic contributions of the gas stream, accretion disk, and any hot spots. Synthetic spectra will be calculated with her synthesis code and compared with observed spectra to derive the physical properties of the separate components of the accretion flows. The derived gas properties will be used to generate hydrodynamic simulations of the binary. Finally, Doppler tomography will be used to visualize the transferred gas and to examine the quality of the derived parameters. The results of this research are expected to have implications for the entire field of interacting binaries. Dr. Richards has already released her new spectrum synthesis code freely to the astronomical community, and other astronomers have published papers after using this code. She also has extensive outreach experience, and she will continue her commitment to outreach activities and maintain numerous interactions with graduate students, undergraduates, K-12 students, teachers, summer high school enrichment programs, and the general public. She also has opportunities to travel around the country to talk about her research and popular astronomy topics.