Hubble Space Telescope Observations of Nine High-Redshift ESSENCE SupernovaeaaBased in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. This research is associated with proposal GO-9860.,bbBased in part on observations taken at the Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which is operated by AURA under cooperative agreement with the National Science Foundation (NSF).,ccBased in part on observations taken with the Very Large Telescope (VLT) under ESO program 170.A-0519.
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We present broadband light curves of nine supernovae ranging in redshift from 0.5 to 0.8. The supernovae were discovered as part of the ESSENCE project, and the light curves are a combination of Cerro Tololo 4 m and Hubble Space Telescope (HST) photometry. On the basis of spectra and/or light-curve fitting, eight of these objects are definitely Type la supernovae, while the classification of one is problematic. The ESSENCE project is a 5 yr endeavor to discover about 200 high-redshift Type la supernovae, with the goal of tightly constraining the time average of the equation-of-state parameter [w = p/(c 2)] of the "dark energy." To help minimize our systematic errors, all of our ground-based photometry is obtained with the same telescope and instrument. In 2003 the highest redshift subset of ESSENCE supernovae was selected for detailed study with HST. Here we present the first photometric results of the survey. We find that all but one of the ESSENCE supernovae have slowly declining light curves and that the sample is not representative of the low-redshift set of ESSENCE Type la supernovae. This is unlikely to be a sign of evolution in the population. We attribute the decline-rate distribution of HST events to a selection bias at the high-redshift edge of our sample and find that such a bias will infect other magnitude-limited Type la supernova searches unless appropriate precautions are taken. 2005. The American Astronomical Society. All rights reserved.
author list (cited authors)
Krisciunas, K., Garnavich, P. M., Challis, P., Prieto, J. L., Riess, A. G., Barris, B., ... Wood-Vasey, W. M.
complete list of authors
Krisciunas, Kevin||Garnavich, Peter M||Challis, Peter||Prieto, Jose Luis||Riess, Adam G||Barris, Brian||Aguilera, Claudio||Becker, Andrew C||Blondin, Stephane||Chornock, Ryan||Clocchiatti, Alejandro||Covarrubias, Ricardo||Filippenko, Alexei V||Foley, Ryan J||Hicken, Malcolm||Jha, Saurabh||Kirshner, Robert P||Leibundgut, Bruno||Li, Weidong||Matheson, Thomas||Miceli, Anthony||Miknaitis, Gajus||Rest, Armin||Salvo, Maria Elena||Schmidt, Brian P||Smith, R Chris||Sollerman, Jesper||Spyromilio, Jason||Stubbs, Christopher W||Suntzeff, Nicholas B||Tonry, John L||Wood-Vasey, W Michael