Program: GS-2004B-Q-4

We have been granted time through the NOAO Survey program to find and follow $\sim$200 Type Ia supernovae (SNe Ia) with the MOSAIC Imager on the Blanco 4-m over a 5yr period (2002B-2006B). Gemini resources, which are not covered by the NOAO Survey program, are needed to provide the critical spectroscopic classifications of the SNe Ia. Our survey will find supernovae distributed evenly over the redshift range [0.15, 0.75]. We aim to answer a simple, but very important, question: is the dark energy of the Universe consistent with a cosmological constant ($w=-1$)? If not, this means the dark energy is likely to be a more general rolling scalar field such as ``quintessence.'' The proposed Gemini GMOS spectra will sort the SNe Ia from other SNe, hypernovae, and AGN, and we will be able to measure accurate supernova rates as a function of lookback time to almost half the age of the Universe. For some core-collapse SNe, we will be able to derive distances through the expanding photosphere method, a critical cross-check for the distance methods. The spectral classifications will be announced immediately to allow other teams to monitor the SNe discovered.