Program: GS-2009B-Q-40

In Chile we have founded the Millennium Center for Supernova Science (MCSS) with the purpose to refine methods for extragalactic distances, study the origin of the dark energy, and to gain a deeper understanding of the physics of these cosmic explosions. A main goal of the MCSS is to secure spectrophotometric observations of supernovae (SNe) at early and late phases. With this proposal we request 50 hours with GMOS. Twenty of these hours are requested as rapid ToO time in order to obtain a detailed time-series (8-10) of optical spectra for two young Type Ia SNe discovered by our CHASE SN search. Through modeling this time-series of early phase spectra, we can determine the abundance stratification of elements in the outer half of the ejecta. With such an analysis we can study the degree of mixing and abundances of intermediate mass elements. This knowledge provides stringent constraints on the explosion mechanism(s). Another twenty hours of standard ToO time is requested to continue our successful late phase spectroscopic follow-up. These data are essential for us to map out the inner ejecta near the site of explosion. Combined with early phase observations we can construct an unprecedented description of the ejecta and thus determine physical parameters of the progenitor systems. Finally, 10 hours of Band 3 time is requested to provide spectral classification for SNe discovered by our CHASE survey.