Spectroscopy of High-Redshift Supernovae from the ESSENCE Project: The First 2 Years**Based in part on observations obtained at the Cerro Tololo Inter-American Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF); the European Southern Observatory, Chile (ESO Programme 170.A-0519); the Gemini Observatory, which is operated by AURA under a cooperative agreement with the NSF on behalf of the Gemini partnership (the NSF [United States], the Particle Physics and Astronomy Research Council [United Kingdom], the National Research Council [Canada], CONICYT [Chile], the Australian Research Council [Australia], CNPq [Brazil], and CONICET [Argentina] [programs GN-2002B-Q-14, GN-2003B-Q-14, and GS-2003B-Q-11]); the Magellan Telescopes at Las Campanas Observatory; the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona; and the F. Academic Article

We present the results of spectroscopic observations of targets discovered during the first 2 years of the ESSENCE project. The goal of ESSENCE is to use a sample of 200 Type Ia supernovae (SNe la) at moderate redshifts (0.2 z 0.8) to place constraints on the equation of state of the universe. Spectroscopy not only provides the redshifts of the objects but also confirms that some of the discoveries are indeed SNe Ia. This confirmation is critical to the project, as techniques developed to determine luminosity distances to SNe Ia depend on the knowledge that the objects at high redshift have the same properties as the ones at low redshift. We describe the methods of target selection and prioritization, the telescopes and detectors, and the software used to identify objects. The redshifts deduced from spectral matching of high-redshift SNe Ia with low-redshift SNe Ia are consistent with those determined from host-galaxy spectra. We show that the high-redshift SNe Ia match well with low-redshift templates. We include all spectra obtained by the ESSENCE project, including 52 SNe Ia, five corecollapse SNe, 12 active galactic nuclei, 19 galaxies, four possibly variable stars, and 16 objects with uncertain identifications. 2005. The American Astronomical Society. All rights reserved.

Matheson, T., Blondin, S., Foley, R. J., Chornock, R., Filippenko, A. V., Leibundgut, B., ... Tonry, J. L.

Matheson, Thomas||Blondin, Stéphane||Foley, Ryan J||Chornock, Ryan||Filippenko, Alexei V||Leibundgut, Bruno||Smith, R Chris||Sollerman, Jesper||Spyromilio, Jason||Kirshner, Robert P||Clocchiatti, Alejandro||Aguilera, Claudio||Barris, Brian||Becker, Andrew C||Challis, Peter||Covarrubias, Ricardo||Garnavich, Peter||Hicken, Malcolm||Jha, Saurabh||Krisciunas, Kevin||Li, Weidong||Miceli, Anthony||Miknaitis, Gajus||Prieto, Jose Luis||Rest, Armin||Riess, Adam G||Salvo, Maria Elena||Schmidt, Brian P||Stubbs, Christopher W||Suntzeff, Nicholas B||Tonry, John L

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