Search

We have developed a new tool for measurement of the cosmological parameters: a systematic search-and-study technique for high-redshift supernovae. In the first years of this Supernova Cosmology Project, we have discovered over 27 supernovae. Using a “batch” search strategy, almost all were discovered before maximum light and were observed over the peak of their light curves. The spectra and light curves indicate that almost all were Type Ia supernovae at redshifts z = 0.35 – 0.65. These high-redshift supernovae can provide a distance indicator and “standard clock” to study the cosmological parameters q 0 , Λ, Ω 0 , and H 0 . This presentation and the following presentation of Goldhaber et al . (1996), will discuss observation strategies and rates, analysis and calibration issues, the sources of measurement uncertainty, and the cosmological implications, including bounds on q 0 , of the first 7 high-redshift supernovae from our ongoing search. This is one of the most direct approaches to cosmological measurements, and could become a standard method in the field.

Alhough there is little doubt at present that the redshift of distant galaxies is due to an expansion of the universe, we present in this paper a direct confirmation for the cosmological expansion. This work is based on the first results from a systematic search for high redshift Type Ia supernovae. We discovered over twenty seven SNe, before or at maximum light. In this paper we report on the first seven of these, with redshift z = 0.35 – 0.46. Type Ia SNe are known to be a homogeneous group of SNe, to first order, with very similar light curves, spectra and peak luminosities. In this paper we report that the light curves we observe are all broadened (time dilated) as expected from the expanding universe hypothesis. Small variations from the expected 1 + z broadening of the light curve widths can be attributed to a width-brightness correlation that has been observed for nearby SNe ( z

We have begun a program to discover high-redshift supernovae ( z ≈ 0.2–0.6), and study them with follow-up photometry and spectroscopy. We report here our first discovery, a supernova at z = 0.458 (SN1992bi) and the ongoing analysis on several new supernova candidates found in a recent search (Dec 93 – March 94). The photometry for SN1992bi closely matches the lightcurve calculated for its redshift from the template of well-observed nearby Type la supernovae giving a best fit value for the deceleration parameter: q o = 0.1 ± 0.3 (±0.55) (with Λ = 0), where the first uncertainty is due to the photometry of the distant supernova and the second reflects the estimated intrinsic width of the Type la absolute magnitude distribution based on nearby supernovae. If there is significant host galaxy extinction then q o would be larger than this best fit value. We describe the main sources of measurement error inherent in such a measurement of qo , and ways to reduce these errors.