230 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
The oldest X-ray supernovae: X-ray emission from 1941C, 1959D, 1968D
We have studied the X-ray emission from four historical Type-II supernovae
(the newly-discovered 1941C in NGC 4631 and 1959D in NGC 7331; and 1968D, 1980K
in NGC 6946), using Chandra ACIS-S imaging. In particular, the first three are
the oldest ever found in the X-ray band, and provide constraints on the
properties of the stellar wind and circumstellar matter encountered by the
expanding shock at more advanced stages in the transition towards the remnant
phase. We estimate emitted luminosities ~ 5 x 10^{37} erg/s for SN 1941C, ~ a
few x 10^{37} erg/s for SN 1959D, ~ 2 x 10^{38} erg/s for SN 1968D, and ~ 4 x
10^{37} erg/s for SN 1980K, in the 0.3-8 keV band. X-ray spectral fits to SN
1968D suggest the presence of a harder component, possibly a power law with
photon index ~ 2, contributing ~ 10^{37} erg/s in the 2-10 keV band. We
speculate that it may be evidence of non-thermal emission from a Crab-like
young pulsar.Comment: 6 pages, accepted by ApJ. Revised version with a couple of added
references. Thanks to A. Kong and E. Schlegel for their comments. Credit to
Holt et al. (2003) for the X-ray discovery of SN 1968D, overlooked in other
recent catalog
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
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
Marsupial extension in terrestrial isopods (Crustacea, Isopoda, Oniscidea)
In Oniscidea, the marsupium is a ventral pouch where the offspring develop independently of an external water source. The marsupium is formed by five pairs of overlapping oostegites that develop in the females during their reproductive period. In this study, ovigerous females of 35 species were dissected, their oostegites were extracted, and the intra-marsupial offspring were counted. Two marsupium forms were recognized: distended, in which the oostegites protrude distally in relation to the sternites; and non-distended, in which the oostegites are parallel to the sixth and seventh sternites. Armadillidium nasatum, A. vulgare, Pudeoniscus birabeni, Circoniscus gaigei and Cubaris murina, conglobating species with a non-distended marsupium, and Neotroponiscus daguerri and N. carolii, non-conglobating species with a distended marsupium, have a concavity on the ventral floor of the 6th and 7th pereionites, here called the marsupial extension. This is the first record of a marsupial extension which extends beyond the area formed by the oostegites in Oniscidea
The bright galaxy population of five medium redshift clusters. I. Color-Magnitude Relation, Blue Fractions and Visual Morphology
Using data of five clusters of galaxies within the redshift range 0.15
z 0.25, imaged with the Nordic Optical Telescope (NOT) in the central
1 Mpc in very good seeing conditions, we have performed an
exhaustive inspection of their bright galaxy population. That range of
redshift, where only a small amount of data with the required resolution and
quality is available, is particularly important for the understanding of the
formation and evolution of clusters of galaxies. We have inspected the
color-magnitude relation (CMR) for those clusters and measured the blue
fraction of galaxies in their cores to check for evidence of evolution as found
in other works. Moreover, the visual classification of the galaxy morphology
has been performed and the morphology-radius relation has been examined We have
not found signs of evolution neither in the slope of the CMR nor in the blue
fraction of galaxies. A diversity of situations regarding those parameters and
in the morphological mixing has been noticed, with two out of five clusters
containing a dominant late-type core population. The cluster A1878 stands out
as some of its properties differ from those of the other clusters in the
sample.
No clear signs of evolution appear in our analysis. The data support the view
that the morphology and the stellar content of the galaxies in our clusters
have been already settled at z 0.2. Only the fraction of interacting
galaxies in the clusters appear to be larger than in clusters like Coma
although the number of clusters in the sample is small to give a definitive
conclusion.Comment: 16 pages, 8 figures, 4 tables, 1 longtable The paper has been already
accepted but still not publishe
The collimated outflows of the planetary nebula Hu1-2: proper motion and radial velocity measurements
Hu\,1-2 is a planetary nebula that contains an isolated knot located
northwestern of the main nebula, which could be related to a collimated
outflow. We present a subsarcsecond H+[N\,{\sc ii}] image and a
high-resolution, long-slit spectrum of Hu\,1-2 that allow us to identify the
southeastern counterpart of the northwestern knot and to establish their high
velocity ( 340 km\,s), collimated bipolar outflow nature. The
detection of the northwestern knot in POSS red plates allows us to carry out a
proper motion analysis by combining three POSS red plates and two narrow-band
H+[N\,{\sc ii}] CCD images, with a time baseline of 57 yr. A
proper motion of 20 6\,mas\,yr along position angle 312
15, and a dynamical age of 1375\llap{}\,yr
are obtained for the bipolar outflow. The measured proper motion and the
spatio-kinematical properties of the bipolar outflow yield a lower limit of
2.7\,kpc for the distance to Hu\,1-2.Comment: 6 pages, 4 figures; accepted for publication in MNRA
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
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
The Evolution of Nova V382 Vel 1999
We report results of spectroscopic observations of V382 Vel (Nova Vel 1999)
carried out at La Silla between 5 and 498 days after maximum light (23 May
1999, V(max) ). The analysis of the photometric and
spectroscopic evolution shows this object to be a {\sl fast nova} belonging to
the Fe II {\sl broad} spectroscopic class. A distance of 1.7 kpc () is
derived from the maximum magnitude vs. rate of decline relationship after
correcting for the small reddening toward the nova, E(B--V)\lsim 0.10. From
the measured H flux and the associated rate of expansion we derive an
approximate mass for the ejected shell, M_{env}\lsim 10^{-5} M. We
have also observed during the early decline a broad, short-lived (\lsim 10
days) feature at 6705-6715 \AA for which several identifications are possible,
one of which is the lithium doublet at 6708 \AA and which could place an
empirical limit on the lithium production that might occur during the outburst
of a {\sl fast nova}. The high luminosity at maximum, M, and the
relatively small height above the galactic plane (z\lsim 160pc) suggest that
V382 Vel originated from a massive white dwarf, likely in the mass range
1.1--1.2 M.Comment: 13 pages + 9 plots(gif). Accepted by A&
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