216 research outputs found
Constraints on Cosmological Models from Hubble Space Telescope Observations of High-z Supernovae
We have coordinated Hubble Space Telescope photometry with ground-based
discovery for three supernovae: two SN Ia near z~0.5 (SN 1997ce, SN 1997cj) and
a third event at z=0.97 (SN 1997ck). The superb spatial resolution of HST
separates each supernova from its host galaxy and leads to good precision in
the light curves. The HST data combined with ground-based photometry provide
good temporal coverage. We use these light curves and relations between
luminosity, light curve shape, and color calibrated from low-z samples to
derive relative luminosity distances which are accurate to 10% at z~0.5 and 20%
at z=1. The redshift-distance relation is used to place constraints on the
global mean matter density, Omega_matter, and the normalized cosmological
constant, Omega_Lambda. When the HST sample is combined with the distance to SN
1995K (z=0.48), analyzed by the same precepts, it suggests that matter alone is
insufficient to produce a flat Universe. Specifically, for
Omega_matter+Omega_Lambda=1, Omega_matter is less than 1 with >95% confidence,
and our best estimate of Omega_matter is -0.1 +/- 0.5 if Omega_Lambda=0.
Although the present result is based on a very small sample whose systematics
remain to be explored, it demonstrates the power of HST measurements for high
redshift supernovae.Comment: Submitted to ApJ Letters, 3 figures, 1 plate, additional tabl
Tooth development and replacement in the Atlantic Cutlassfish, Trichiurus lepturus, with comparisons to other Scombroidei
Atlantic Cutlassfish, Trichiurus lepturus, have large, barbed, premaxillary and dentary fangs, and sharp dagger-shaped teeth in their oral jaws. Functional teeth firmly ankylose to the dentigerous bones. We used dry skeletons, histology, SEM, and micro-CT scanning to study 92 specimens of T. lepturus from the western North Atlantic to describe its dentition and tooth replacement. We identified three modes of intraosseous tooth replacement in T. lepturus depending on the location of the tooth in the jaw. Mode 1 relates to replacement of premaxillary fangs, in which new tooth germs enter the lingual surface of the premaxilla, develop horizontally, and rotate into position. We suggest that growth of large fangs in the premaxilla is accommodated by this horizontal development. Mode 2 occurs for dentary fangs: new tooth germs enter the labial surface of the dentary, develop vertically, and erupt into position. Mode 3 describes replacement of lateral teeth, in which new tooth germs enter a trench along the crest of the dentigerous bone, develop vertically, and erupt into position. Such distinct modes of tooth replacement in a teleostean species are unknown. We compared modes of replacement in T. lepturus to 20 species of scombroids to explore the phylogenetic distribution of these three replacement modes. Alternate tooth replacement (in which new teeth erupt between two functional teeth), ankylosis, and intraosseous tooth development are plesiomorphic to Bluefish + other Scombroidei. Our study highlights the complexity and variability of intraosseous tooth replacement. Within tooth replacement systems, key variables include sites of formation of tooth germs, points of entry of tooth germs into dentigerous bones, coupling of tooth germ migration and bone erosion, whether teeth develop horizontally or immediately beneath the tooth to be replaced, and how tooth eruption and ankylosis occur. Developmentally different tooth replacement processes can yield remarkably similar dentitions
Hypervelocity Stars II. The Bound Population
Hypervelocity stars (HVSs) are stars ejected completely out of the Milky Way
by three-body interactions with the massive black hole in the Galactic center.
We describe 643 new spectroscopic observations from our targeted survey for
HVSs. We find a significant (3.5 sigma) excess of B-type stars with large
velocities +27510 kpc that are most plausibly
explained as a new class of HVSs: stars ejected from the Galactic center on
bound orbits. If a Galactic center ejection origin is correct, the distribution
of HVSs on the sky should be anisotropic for a survey complete to a fixed
limiting apparent magnitude. The unbound HVSs in our survey have a marginally
anisotropic distribution on the sky, consistent with the Galactic center
ejection picture.Comment: 8 pages, accepted to Ap
Knockout mice: Is it just genetics? Effect of enriched housing on fibulin-4+/- mice
Background. Fibulin-4 is an extracellular matrix protein expressed by vascular smooth muscle cells that is essential for maintaining arterial integrity. Fibulin-4-/- mice die just before birth due to arterial hemorrhage, but fibulin-4+/- mice appear to be outwardly normal. Experiments were therefore performed to determine whether fibulin-4+/- mice display arterial pathologies on a microscopic scale. After preliminary experiments were performed, a second purpose developed, which was to test the hypothesis that any observed pathologies would be ameliorated by housing the animals in enriched cages. Methodology. Fibulin-4+/- and wild-type mice were housed either four/cage in standard cages or two per cage in larger cages, each cage containing a tunnel and a wheel. After three weeks the mice were sacrificed, and the aortas perfusion-fixed and excised for light and electron microscopy. Principle Findings. When the mice were in standard cages, localized regions of disorganized extracellular matrix and collagen fibers consistently appeared between some of the medial smooth muscle cells in the fibulin-4+/- mice. In the wild-type mice, the smooth muscle cells were closely connected to each other and the media was more compact. The number of disorganized regions per square mm was significantly greater for fibulin-4+/- mice (172±43 (SEM)) than for wild-type mice (15±8) (p<0.01, n = 8). When the mice were in enriched cages, the fibulin-4+/- mice showed significantly fewer disorganized regions than those in standard cages (35±12) (p<0.05, n = 8). The wild type mice also showed fewer disorganized regions (3±2), but this difference was not significant. Conclusions. These results indicate that arterial pathologies manifested in fibulin-4+/- mice can be reduced by enriching the housing conditions, and imply that appropriate environments may counteract the effects of some genetic deficiencies
Palomar Observatory Hale Telescope : Prime Focus Nebular Spectrograph Log Book
The Prime Focus Nebular Spectrograph was used at the Hale Telescope from June 1950 to June 1973 -- a span of 33 years -- by which time it was supplanted by Cassegrain spectrographs equipped with image intensifiers.
In 1981, the instrument (without the two semi-solid Bowen-Schmidt cameras) was given on a long-term loan to the Jet Propulsion Laboratory for use at the Table Mountain Observatory.
This book consists of copies of the observing log in which the exposures were recorded. The two original log books have been deposited in the Caltech Archive
The Hubble Constant
I review the current state of determinations of the Hubble constant, which
gives the length scale of the Universe by relating the expansion velocity of
objects to their distance. There are two broad categories of measurements. The
first uses individual astrophysical objects which have some property that
allows their intrinsic luminosity or size to be determined, or allows the
determination of their distance by geometric means. The second category
comprises the use of all-sky cosmic microwave background, or correlations
between large samples of galaxies, to determine information about the geometry
of the Universe and hence the Hubble constant, typically in a combination with
other cosmological parameters. Many, but not all, object-based measurements
give values of around 72-74km/s/Mpc , with typical errors of 2-3km/s/Mpc.
This is in mild discrepancy with CMB-based measurements, in particular those
from the Planck satellite, which give values of 67-68km/s/Mpc and typical
errors of 1-2km/s/Mpc. The size of the remaining systematics indicate that
accuracy rather than precision is the remaining problem in a good determination
of the Hubble constant. Whether a discrepancy exists, and whether new physics
is needed to resolve it, depends on details of the systematics of the
object-based methods, and also on the assumptions about other cosmological
parameters and which datasets are combined in the case of the all-sky methods.Comment: Extensively revised and updated since the 2007 version: accepted by
Living Reviews in Relativity as a major (2014) update of LRR 10, 4, 200
Properties of Blood, Porphyrins, and Exposure to Legacy and Emerging Persistent Organic Pollutants in Surf Scoters (Melanitta perspicillata) Overwintering on the South Coast of British Columbia, Canada
The surf scoter (Melanitta perspicillata) is a little-studied species of North American sea duck. Estimates suggest it has experienced a precipitous decline in breeding numbers over the latter half of the past century. To investigate the potential role of contaminant uptake and toxicity in the population decline, this study undertook to measure blood chemistry, porphyrin concentrations, EROD, and organic contaminants in mature surf scoters wintering in the Strait of Georgia, BC, Canada. Hepatic organochlorine pesticide, polychlorinated dibenzo-p-dioxin, polychlorinated dibenzofuran, polychlorinated biphenyl (PCB), polybrominated diphenyl ether, and nonylphenol concentrations were relatively low; for example, ÎŁTEQs (toxic equivalents) for PCBs, dioxins, and furans combined ranged from 4.7Â ng/kg wet weight in reference-site (Baynes Sound) birds to 11.4Â ng/kg wet weight in birds from Vancouver Harbour. Nonetheless, elevated EROD activity indicated that birds in Howe Sound were responding to an Ah-receptor-mediated stressor, which was also affecting hematocrit values and possibly vitamin A status. In addition, a low proportion of lymphocytes in individuals across locations in early spring samples was associated with poor body condition. The apparent loss of fitness just prior to the onset of northerly migrations to breeding grounds is of particular concern. Compromised health of mature birds at this point in the season might impact negatively on the productivity and survival of some individuals, particularly those overwintering in Howe Sound
Allan Sandage and the Cosmic Expansion
This is an account of Allan Sandage's work on (1) The character of the
expansion field. For many years he has been the strongest defender of an
expanding Universe. He later explained the CMB dipole by a local velocity of
220 +/- 50 km/s toward the Virgo cluster and by a bulk motion of the Local
supercluster (extending out to ~3500 km/s) of 450-500 km/s toward an apex at
l=275, b=12. Allowing for these streaming velocities he found linear expansion
to hold down to local scales (~300 km/s). (2) The calibration of the Hubble
constant. Probing different methods he finally adopted - from
Cepheid-calibrated SNe Ia and from independent RR Lyr-calibrated TRGBs - H_0 =
62.3 +/- 1.3 +/- 5.0 km/s/Mpc.Comment: 12 pages, 11 figures, 1 table, Submitted to Astrophysics and Space
Science, Special Issue on the Fundamental Cosmic Distance Scale in the Gaia
Er
The zCOSMOS redshift survey: the three-dimensional classification cube and bimodality in galaxy physical properties
Aims. We investigate the relationships between three main optical galaxy
observables (spectral properties, colours, and morphology), exploiting the data
set provided by the COSMOS/zCOSMOS survey. The purpose of this paper is to
define a simple galaxy classification cube, using a carefully selected sample
of around 1000 galaxies. Methods. Using medium resolution spectra of the first
1k zCOSMOS-bright sample, optical photometry from the Subaru/COSMOS
observations, and morphological measurements derived from ACS imaging, we
analyze the properties of the galaxy population out to z~1. Applying three
straightforward classification schemes (spectral, photometric, and
morphological), we identify two main galaxy types, which appear to be linked to
the bimodality of galaxy population. The three parametric classifications
constitute the axes of a "classification cube". Results. A very good agreement
exists between the classification from spectral data (quiescent/star-forming
galaxies) and that based on colours (red/blue galaxies). The third parameter
(morphology) is less well correlated with the first two: in fact a good
correlation between the spectral classification and that based on morphological
analysis (early-/late-type galaxies) is achieved only after partially
complementing the morphological classification with additional colour
information. Finally, analyzing the 3D-distribution of all galaxies in the
sample, we find that about 85% of the galaxies show a fully concordant
classification, being either quiescent, red, bulge-dominated galaxies (~20%) or
star-forming, blue, disk-dominated galaxies (~65%). These results imply that
the galaxy bimodality is a consistent behaviour both in morphology, colour and
dominant stellar population, at least out to z~1.Comment: 11 pages, Accepted for publication in A&
- âŠ