Showing papers by "I. M. Hook published in 1997"

Measurements* of the Cosmological Parameters Ω and Λ from the First Seven Supernovae at z ≥ 0.35

Abstract: We have developed a technique to systematically discover and study high-redshift supernovae that can be used to measure the cosmological parameters. We report here results based on the initial seven of more than 28 supernovae discovered to date in the high-redshift supernova search of the Supernova Cosmology Project. We find an observational dispersion in peak magnitudes of ? -->MB=0.27; this dispersion narrows to ?MB, corr=0.19 after correcting the magnitudes using the light-curve width-luminosity relation found for nearby (z ? 0.1) Type Ia supernovae from the Cal?n/Tololo survey (Hamuy et al.). Comparing light-curve width-corrected magnitudes as a function of redshift of our distant (z = 0.35-0.46) supernovae to those of nearby Type Ia supernovae yields a global measurement of the mass density, ?M${r M}$ -->=0.88 -->+ 0.69?0.60 for a ? = 0 cosmology. For a spatially flat universe (i.e., ?M + ?? = 1), we find ?M${r M}$ -->=0.94 -->+ 0.34?0.28 or, equivalently, a measurement of the cosmological constant, ??=0.06 -->+ 0.28?0.34 ( < 0.51 at the 95% confidence level). For the more general Friedmann-Lema?tre cosmologies with independent ?M and ??, the results are presented as a confidence region on the ?M-?? plane. This region does not correspond to a unique value of the deceleration parameter q0. We present analyses and checks for statistical and systematic errors and also show that our results do not depend on the specifics of the width-luminosity correction. The results for ??-versus-?M are inconsistent with ?-dominated, low-density, flat cosmologies that have been proposed to reconcile the ages of globular cluster stars with higher Hubble constant values.

Implications for the Hubble Constant from the First Seven Supernovae at z >= 0.35

Abstract: The Supernova Cosmology Project has discovered over 28 supernovae (SNs) at 0.35 < z < 0.65 in an ongoing program that uses Type Ia SNs (SN Ia's) as high-redshift distance indicators. Here we present measurements of the ratio between the locally observed and global Hubble constants, HL0/HG0, based on the first seven SNs of this high-redshift data set compared with 18 SNs at z ≤ 0.1 from the Calan/Tololo survey. If ΩM ≤ 1, then light-curve width corrected SN magnitudes yield HL0/HG0 < 1.10 (95% confidence level) in both a Λ = 0 and a flat universe. The analysis using the SN Ia's as standard candles without a light-curve width correction yields similar results. These results rule out the hypothesis that the discrepant ages of the Universe derived from globular clusters and recent measurements of the Hubble constant are attributable to a locally underdense bubble. Using the Cepheid-distance-calibrated absolute magnitudes for SN Ia's of Sandage et al., we can also measure the global Hubble constant, HG0. If ΩM ≥ 0.2, we find that HG0 < 70 km s-1 Mpc-1 in a Λ = 0 universe and HG0 < 78 km s-1 Mpc-1 in a flat universe, correcting the distant and local SN apparent magnitudes for light-curve width. Lower results for HG0 are obtained if the magnitudes are not width-corrected.

Observation of Cosmological Time Dilation Using Type Ia Supernovae as Clocks

Abstract: This work is based on the first results from a systematic search for high redshift Type Ia supernovae. Using filters in the R-band we discovered seven such SNe, with redshift z = 0.3 — 0.5, before or at maximum light. 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 talk 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 < 0.1). We show in this talk the first clear observation of the cosmological time dilation for macroscopic objects.

Scheduled Discoveries of 7+ High-Redshift Supernovae:First Cosmology Results and Bounds on q 0

Abstract: Our search for high-redshift Type Ia supernovae discovered, in its first years, a sample of seven 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 - 0.5. These high-redshift supernovae can provide a distance indicator and ``standard clock`` to study the cosmological parameters q{sub 0} , {Lambda}, {Omega}{sub 0} , and H{sub 0}. This presentation and the following presentations of Kim et al. (1996), Goldhaber et al. (1996), and Pain 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{sub 0} , of these first high-redshift supernovae from our ongoing search.