R-band intensity measurements along the light curve of Type Ia supernovae discovered by the Supernova Cosmology Project (SCP) are fitted in brightness to templates allowing a free parameter the time-axis width factor w ≡ s × (1 + 2 z). The data points are then individually aligned in the time-axis, normalized and K-corrected back to the rest frame, after which the nearly 1300 normalized intensity measurements are found to lie on a well-determined common rest-frame B-band curve which we call the "composite curve". The same procedure is applied to 18 low-redshift Calán/Tololo SNe with z < 0.11; these nearly 300 B-band photometry points are found to lie on the composite curve equally well. The SCP search technique produces several measurements before maximum light for each supernova. We demonstrate that the linear stretch factor, s, which parameterizes the light-curve timescale appears independent of z, and applies equally well to the declining and rising parts of the light curve. In fact, the B band template that best fits this composite curve fits the individual supernova photometry data when stretched by a factor s with χ 2 /DoF ≈ 1, thus as well as any parameterization can, given the current data sets. The measurement of the date of explosion, however, is model dependent and not tightly constrained by the current data. We also demonstrate the 1 + z light-curve time-axis broadening expected from cosmological expansion. This argues strongly against alternative explanations, such as tired light, for the redshift of distant objects.
We present results from a study of the photometric redshift performance of the Dark Energy Survey (DES), using the early data from a Science Verification (SV) period of observations in late 2012 and early 2013 that provided science-quality images for almost 200 sq. deg. at the nominal depth of the survey. We assess the photometric redshift (photo-z) performance using about 15000 galaxies with spectroscopic redshifts available from other surveys. These galaxies are used, in different configurations, as a calibration sample, and photo-z's are obtained and studied using most of the existing photo-z codes. A weighting method in a multi-dimensional color-magnitude space is applied to the spectroscopic sample in order to evaluate the photo-z performance with sets that mimic the full DES photometric sample, which is on average significantly deeper than the calibration sample due to the limited depth of spectroscopic surveys. Empirical photo-z methods using, for instance, Artificial Neural Networks or Random Forests, yield the best performance in the tests, achieving core photo-z resolutions σ 68 ∼ 0.08. Moreover, the results from most of the codes, including template fitting methods, comfortably meet the DES requirements on photo-z performance, therefore, providing an excellent precedent for future DES data sets.
Heat-capacity, X-ray diffraction, and resistivity measurements on a high-quality BaFe2As2 sample show an evolution of the magneto-structural transition with successive annealing periods. After a 30-day anneal the resistivity in the (ab) plane decreases by more than an order of magnitude, to 12 µΩcm, with a residual resistance ratio ∼36; the heat-capacity anomaly at the transition sharpens, to an overall width of less than K, and shifts from 135.4 to 140.2 K. The heat-capacity anomaly in both the as-grown sample and after the 30-day anneal shows a hysteresis of ∼0.15 K, and is unchanged in a magnetic field µ0H = 14 T. The X-ray and heat-capacity data combined suggest that there is a first order jump in the structural order parameter. The entropy of the transition is reported.
The electronic phase diagram of PrFeAsO1−xFx (0≤x≤0.225) has been determined using synchrotron X-ray powder diffraction, magnetization and resistivity measurements. The structural transition temperature is suppressed from 154 K to ≈120 K and the magnetic phase transitions of both iron and praseodymium ions are completely suppressed by x≈0.08 fluorine doping, coinciding with the emergence of superconductivity. The optimal doping is x≈0.15 when TC =47 K, while the maximum solubility of fluorine in PrFeAsO1−xFx is reached around x=0.22. The structural, magnetic and superconducting phase diagram is presented.
Abstract. This work is based on the rst results from a systematic search for high redshift Type Ia supernovae. Using lters 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 rst 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 rst clear observation of the cosmological time dilation for macroscopic objects.
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