Joseph A. Nuth
Laboratory Astrophysics is Not an Oxymoron
There is no need to duplicate the exact conditions found in an astrophysical environment in order to perform experiments that yield interesting and very pertinent results. Laboratory astrophysics supplies the basic data required to model processes in astrophysical settings and occasionally reveals surprising behavior in physical systems that require more sophisticated explanations than initially expected. Three examples will be presented in order to demonstrate the utility of laboratory measurements in understanding astrophysical observations. First, laboratory studies designed to measure the vapor pressure of SiO molecules, the basic building block of silicate grains that condense in the outflows of oxygen rich stars will be presented. Second, experiments conducted to measure the efficiency of the growth of crystalline grains from atomic vapors will be described. Such grains might form at equilibrium in the atmospheres of AGB stars before a significant stellar wind has developed. These experiments were performed on NASA’s KC-135 Reduced Gravity Research aircraft to minimize the effects of thermally induced convection. Finally, a completely unexpected phenomenon observed during the condensation of Fe-Mg-SiO vapors will be discussed: condensate compositions controlled at metastable eutectic points in the MgO-FeO-SiO phase diagram. These experiments imply the formation of separate populations of iron silicate and magnesium silicate grains from a mixed vapor of iron, magnesium and SiO that would be found in typical stellar outflows and have interesting implications for observations of crystalline magnesium silicate minerals in high mass loss stars.