Oral, Thursday, January 13, 2000, 10:00-11:30am, Regency VII

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*Y. Wang (Univ. of Notre Dame)*

Because of flux conservation, flux-averaging *justifies*
the use of the distance-redshift relation for a smooth
universe in the analysis of type Ia supernova (SN Ia) data.
We have combined the SN Ia data from the High-z SN Search
and the Supernova Cosmology Project, and binned the combined
data by flux-averaging in redshift intervals of \Delta
z=0.05 and \Delta z=0.1. We find that the unbinned data
yield a Hubble constant of H_{0}=65±
1\,km\,s^{-1}\,Mpc^{-1} (statistical error only), a
matter density fraction of \Omega_{m}=0.7±.4, and a
vacuum energy density fraction of
\Omega_{\Lambda}=1.2±.5. The binned data for \Delta
z=0.1 yield H_{0}=65±1\,km\,s^{-1}\,Mpc^{-1}
(statistical error only), \Omega_{m}=0.3±.6, and
\Omega_{\Lambda}=0.7±.7. Our results are not sensitive
to the redshift bin size. Flux-averaging leads to less
biased estimates of the cosmological parameters by reducing
the bias due to systematic effects such as weak lensing.

Comparison of the data of 18 SNe Ia published by both groups
yields a mean SN Ia peak absolute magnitude of
M_{B}=-19.33±0.25. The internal dispersion of each data
set is about 0.20 magnitude in the *calibrated* SN Ia
peak absolute magnitudes. The difference in analysis
techniques introduces an additional uncertainty of about
0.15 magnitude.

If the SNe Ia peak absolute luminosity changes with redshift
due to evolution, our ability to measure the cosmological
parameters from SN Ia data will be significantly diminished.
Assuming power-law evolution in the peak absolute
luminosity, (1+z)^{\beta}, we find a strong degeneracy
between the evolution power-law index \beta and the matter
density fraction \Omega_{m}. For \Omega_{m}=0.3, we find
that the unbinned data yields H_{0}=65±
1\,km\,s^{-1}\,Mpc^{-1} (statistical error only),
\Omega_{\Lambda}=1.4±1.1, and \beta=0.5±1.6, and
the binned data (with \Delta z=0.1) yields H_{0}=65±
1\,km\,s^{-1}\,Mpc^{-1} (statistical error only),
\Omega_{\Lambda}=0.6±1.4, and \beta=0.0±1.0.

If you would like more information about this abstract, please follow the link to http://www.nd.edu/~ywang5/public/. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser. [Previous] | [Session 55] | [Next]