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R. J. Foley (UC Berkeley), ESSENCE Collaboration
We present the results of the first four years of spectroscopic observations of targets discovered by the Equation of State: SupErNovae trace Cosmic Expansion (ESSENCE) project. The goal of ESSENCE is to use a sample of 200 Type Ia supernovae (SNe Ia) in the redshift range 0.2 < z < 0.8 to place constraints on the equation of state of the Universe. Spectroscopy not only provides the redshift of the object, but also confirmation that the discoveries are SNe Ia. This confirmation is critical to the project, as techniques developed to determine luminosity distances to SNe Ia depend upon the knowledge that the objects at high redshift are the same as the ones at low redshift. We describe our new method of estimating the likelihood of an SN to be of type Ia. Analysis of multi-epoch spectra and high S/N spectra reveals that high-redshift SNe Ia are spectroscopically consistent and their spectra evolve similarly to low-redshift SNe Ia, showing no signs of evolution from z ~0.8 to z = 0.
This work is partially supported by grant AST-0443378 from the US National Science Foundation.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.