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Session 85 - Cosmology: Observations.
Display session, Friday, January 09
Exhibit Hall,

[85.03] Constraints on Cosmological Models from Hubble Space Telescope Observations of High-z Supernovae

P. M. Garnavich, R. P. Kirshner, P. Challis (CfA), J. Tonry (UHawaii), R. L. Gilliland (STScI), R. C. Smith (UMich), A. Clocchiatti (CTIO), A. Diercks (UWash), A. V. Filippenko (UCB), M. Hamuy (UAriz), C. J. Hogan (UWash), B. Leibundgut (ESO), M. M. Phillips (CTIO), D. Reiss (UWash), A. G. Riess (UCB), B. P. Schmidt (MSSSO), J. Spyromilio (ESO), C. Stubbs (UWash), N. B. Suntzeff (CTIO), L. Wells (UAriz)

We have coordinated Hubble Space Telescope photometry with ground-based discovery for three supernovae: two SN Ia near z\sim 0.5 (SN 1997ce, SN 1997cj) and a third event at z=0.97 (SN 1997ck). The superb spatial resolution of HST separates each supernova from its host galaxy and leads to good precision in the light curves. The HST data combined with ground-based photometry provide good temporal coverage. We use these light curves and relations between luminosity, light curve shape, and color calibrated from low-z samples to derive relative luminosity distances which are accurate to 10%\ at z\sim 0.5 and 20%\ at z=1. The redshift-distance relation is used to place constraints on the global mean matter density, Ømega_m, and the normalized cosmological constant, Ømega_\Lambda. When the HST\ sample is combined with the distance to SN 1995K (z=0.48), analyzed by the same precepts, it suggests that matter alone is insufficient to produce a flat Universe. Specifically, for Ømega_m+Ømega_\Lambda =1, Ømega_m is less than 1 with >95%\ confidence, and our best estimate of Ømega_m is -0.1 \pm 0.5 if Ømega_\Lambda =0. Although the present result is based on a very small sample whose systematics remain to be explored, it demonstrates the power of HST\ measurements for high redshift supernovae.

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