RSAA Colloquia / Seminars / Feast-of-Facts: Friday, 15 May 2015, 14:00-14:20; Duffield Lecture Theatre

Michael Childress

"Measuring the power source for Type Ia supernovae with late time spectra"

Type Ia supernovae are the thermonuclear explosion of a carbon-oxygen white dwarf. The explosion itself produces half a solar mass of radioactive nickel, whose decay injects energy into the ejecta and powers the bright (M_B ~ -19) optical light curve. We present a new technique for measuring directly the amount of nickel created in the explosion by observing signatures of its daughter nucleus, cobalt, in very late time (t~200 days) spectra. Coupling this to recent work by Richard Scalzo, we find that SNe Ia from white dwarfs below the Chandrasekhar mass consistently produce a modest amount of nickel (~0.5 solar masses) while Chandrasekhar mass white dwarfs produce a broader range (0.4-1.2 solar masses) - this may consistute evidence for two distinct explosion mechanisms. This work makes heavy use of RSAA resources, including new data from the ANU 2.3m telescope (WiFeS), RSAA Keck time (DEIMOS on Keck II), and collaborative work with RSAA Distinguished Visitor John Hillier (Pittsburgh).