AAS 205th Meeting, 9-13 January 2005
Session 69 Cosmology: Population III, Distant SNe, and Dark Energy
Poster, Tuesday, January 11, 2005, 9:20am-6:30pm, Exhibit Hall

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[69.09] The First Photometry from the ESSENCE Project

K. Krisciunas, P. Garnavich (NDU), P. Challis, M. Hicken, R. P. Kirshner, C. Stubbs (CfA), J. L. Prieto (OSU), A. G. Riess (STScI), B. Barris, J. L. Tonry (IfA/UH), C. Aguilera, A. Rest, R. C. Smith, N. B. Suntzeff (CTIO), A. C. Becker, R. Covarrubias, A. Miceli, G. Miknaitis (UW), S. Blondin, B. Leibundgut, J. Spyromilio (ESO), R. Chornock, A. V. Filippenko, S. Jha, W. D. Li (UCB), A. Clocchiatti (PUC), T. Matheson (NOAO), M. E. Salvo, B. P. Schmidt (ANU), J. Sollerman (Stockholm Obs.)

ESSENCE is a 5 year project being carried out on the CTIO 4-m telescope to discover 200 Type Ia supernovae in the redshift range 0.2 to 0.8, with the purpose of estimating the equation of state parameter of the universe (w) to ± 10 percent. In each ESSENCE cycle, we observe the first half of every other night during the dark/grey nights in October, November, and December. We are presently in the third year of the project.

Here we present a selection of nine supernovae discovered and followed by ESSENCE in cycle two and observed by the Hubble Space Telescope (HST). HST is particularly useful in defining the decay after maximum for the highest redshift events in the ESSENCE sample. The preliminary ground-based photometry is in the R- and I-bands, while the HST observations with the Advanced Camera for Surveys were taken in the F625W, F775W, and F850LP filters. The observed photometry is transformed to the rest frame B- and V-bands, from which we derive the reddening, absolute magnitudes at maximum, and luminosity distances. We find that the HST observations start after maximum but their high signal-to-noise are critical in defining the light curve shape for the faint targets at higher redshifts (z > 0.5) discovered with the CTIO 4-m.

The different ground-based and space-based bandpasses present an excellent test of the systematic errors introduced in various photometric systems. We combine these nine objects with those on the current high redshift Hubble diagram and project cosmological constraints that will be obtained from the final ESSENCE data set.

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