Collaborative Research: An integrated experimental and observational study of cosmic silicate astromineralogy

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AST-0908302/0908309Speck/HofmeisterThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Silicate dust is an important component of many astrophysical environments. Spectral features due to "amorphous" silicates have been observed in diverse settings ranging from our solar system and the atmospheres of comets, to the circumstellar ejecta of dying stars, to the environments of active galactic nuclei. Dust plays an essential role in star formation processes, and contributes to several aspects of interstellar processes such as gas heating and the formation of molecules. Since mass-loss from evolved stars is radiation driven, it is intimately linked to the precise nature of the circumstellar dust. However, the effects of composition and structure on the spectra from dust are poorly constrained, leading to ambiguities in interpretation. This project will investigate the laboratory infrared spectra and glass transition temperatures of "amorphous" silicate minerals, providing the necessary spectral and physical property data to constrain dust models. These data will allow a better understanding of the conditions under which various silicates form and are processed in many astrophysical environments, including dying stars of all masses, young stellar objects, and the interstellar medium.A series of laboratory investigations will explore the variation in spectral signatures of well-characterized suites of pyroxenes and melilites, including changes due to solid-solution behavior and variable iron oxidation state. A key outcome will be to determine whether grain types such as glasses, polycrystalline samples, and glass-crystallite mixtures, can in fact be distinguished spectroscopically. The work will provide physical data for silicate glasses and melts, such as glass transition temperature and heat capacity, giving a better understanding of the conditions under which various silicates form and are processed, and the effect of transient heating events. The results will then be used to study the mineralogy of the ejecta of asymptotic giant branch and red supergiant stars, gaining insight into competing dust formation mechanisms, and to find the formation sites of interstellar silicates by testing whether they are glassy or poly-crystalline.This is a cross-disciplinary study involving an astrophysicist, a mineral physicist and an experimental petrologist. The data to be collected are important for studies of silicate melts, which pertain to magmatism on terrestrial planets, and not insignificantly to the glass industry. The cross-fertilization of ideas and techniques provides a broad, interdisciplinary education for the involved graduate students, expanding horizons and promoting thinking outside the box. The female PIs (an under-represented group) are strong role models for women in these fields, and active mentors to younger researchers.