The Case for an Accelerating Universe from Supernovae

The unexpected faintness of high-redshift Type Ia supernovae (SNe Ia), as measured by two teams, has been interpreted as evidence that the expansion of the Universe is accelerating. We review the current challenges to this interpretation and seek to answer whether the cosmological implications are compelling. We discuss future observations of SNe Ia which could offer extraordinary evidence to test acceleration.Comment: To appear as an Invited Review for PASP 20 pages, 13 figure

The Palomar Testbed Interferometer Calibrator Catalog

The Palomar Testbed Interferometer (PTI) archive of observations between 1998 and 2005 is examined for objects appropriate for calibration of optical long-baseline interferometer observations - stars that are predictably point-like and single. Approximately 1,400 nights of data on 1,800 objects were examined for this investigation. We compare those observations to an intensively studied object that is a suitable calibrator, HD217014, and statistically compare each candidate calibrator to that object by computing both a Mahalanobis distance and a Principal Component Analysis. Our hypothesis is that the frequency distribution of visibility data associated with calibrator stars differs from non-calibrator stars such as binary stars. Spectroscopic binaries resolved by PTI, objects known to be unsuitable for calibrator use, are similarly tested to establish detection limits of this approach. From this investigation, we find more than 350 observed stars suitable for use as calibrators (with an additional $\approx 140$ being rejected), corresponding to $\gtrsim 95$ sky coverage for PTI. This approach is noteworthy in that it rigorously establishes calibration sources through a traceable, empirical methodology, leveraging the predictions of spectral energy distribution modeling but also verifying it with the rich body of PTI's on-sky observations.Comment: 100 pages, 7 figures, 7 tables; to appear in the May 2008ApJS, v176n

New Constraints on ΩM\Omega_M, ΩΛ\Omega_\Lambda, and w from an Independent Set of Eleven High-Redshift Supernovae Observed with HST

We report measurements of $\Omega_M$, $\Omega_\Lambda$, and w from eleven supernovae at z=0.36-0.86 with high-quality lightcurves measured using WFPC-2 on the HST. This is an independent set of high-redshift supernovae that confirms previous supernova evidence for an accelerating Universe. Combined with earlier Supernova Cosmology Project data, the new supernovae yield a flat-universe measurement of the mass density $\Omega_M=0.25^{+0.07}_{-0.06}$ (statistical) $\pm0.04$ (identified systematics), or equivalently, a cosmological constant of $\Omega_\Lambda=0.75^{+0.06}_{-0.07}$ (statistical) $\pm0.04$ (identified systematics). When the supernova results are combined with independent flat-universe measurements of $\Omega_M$ from CMB and galaxy redshift distortion data, they provide a measurement of $w=-1.05^{+0.15}_{-0.20}$ (statistical) $\pm0.09$ (identified systematic), if w is assumed to be constant in time. The new data offer greatly improved color measurements of the high-redshift supernovae, and hence improved host-galaxy extinction estimates. These extinction measurements show no anomalous negative E(B-V) at high redshift. The precision of the measurements is such that it is possible to perform a host-galaxy extinction correction directly for individual supernovae without any assumptions or priors on the parent E(B-V) distribution. Our cosmological fits using full extinction corrections confirm that dark energy is required with $P(\Omega_\Lambda>0)>0.99$, a result consistent with previous and current supernova analyses which rely upon the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution.Comment: Accepted for publication in Astrophysical Journal; For data tables and full-resolution figures, see http://supernova.lbl.go

Lactate dehydrogenase activity and isoform distribution in the rat urinary bladder: effects of outlet obstruction and its removal

The rat urinary bladder responded to infravesical obstruction by an increased weight. The weight began to increase after 3 days of obstruction. After 10 days the weight gain had become significant, but increased further with time. At 90 days the bladders weighed 12 times the initial weight. Lactate dehydrogenase (LDH) activity per unit bladder weight increased with the duration of the obstruction. The increase was significant in the 90 day group. The isoform pattern of LDH was determined. For the control group the M3H form was dominant, with M4 second; M4 became the dominant isoform after 3 days of obstruction. The relative amount of M4 had increased by 80% after 90 days. In one group, which was first obstructed for 10 days and then had the obstruction removed for 4 weeks, bladder weight and LDH isoform pattern were normal. We suggest that the changes in isoform pattern in the obstructed bladder reflect a metabolic adaptation to the prolonged voiding time and the increased detrusor pressure, with a consequently compromised oxygen supply, and that the changes are reversible if the outlet conditions are normalized