1,077 research outputs found
Color and Variability Characteristics of Point Sources in the Faint Sky Variability Survey
We present an analysis of the color and variability characteristics for point
sources in the Faint Sky Variability Survey (FSVS). The FSVS cataloged ~23
square degrees in BVI filters from ~16--24 mag to investigate variability in
faint sources at moderate to high Galactic latitudes. Point source completeness
is found to be >83% for a selected representative sample (V=17.5--22.0 mag,
B-V=0.0--1.5) containing both photometric B, V detections and 80% of the
time-sampled V data available compared to a basic internal source completeness
of 99%. Multi-epoch (10--30) observations in V spanning minutes to years
modeled by light curve simulations reveal amplitude sensitivities to
0.015--0.075 mag over a representative V=18--22 mag range. Periodicity
determinations appear viable to time-scales of an order 1 day or less using the
most sampled fields (~30 epochs). The fraction of point sources is found to be
generally variable at 5--8% over V=17.5--22.0 mag. For V brighter than 19 mag,
the variable population is dominated by low amplitude (<0.05 mag) and blue
(B-V<0.35) sources, possibly representing a population of gamma Doradus stars.
Overall, the dominant population of variable sources are bluer than B-V=0.65
and have Main Sequence colors, likely reflecting larger populations of RR
Lyrae, SX Phe, gamma Doradus, and W UMa variables.Comment: 34 pages, 16 figures, accepted in A
Most Rotational Variables Dominated by a Single Bright Feature are CVn Stars
We previously reported a rare class of variable star light curves isolated
from a sample of 4.7 million candidate variables from the ATLAS survey. Dubbed
`UCBH' light curves, they have broad minima and narrow, symmetrical maxima,
with typical periods of 1-10 days and amplitudes of 0.05--0.20 mag. They
maintain constant amplitude, shape, and phase coherence over multiple years,
but do not match any known class of pulsating variables. A localized bright
spot near the equator of a rotating star will produce a UCBH-type light curve
for most viewing geometries. Most stars that exhibit rotational variability
caused primarily by a single bright feature should therefore appear as UCBH
stars, although a rotating bright spot is not the only thing that could produce
a UCBH-type lightcurve. We have spectroscopically investigated fourteen UCBH
stars and found ten of them to be Ap/Bp stars: A-type or B-type stars with
greatly enhanced photospheric abundances of specific heavy elements.
Rotationally variable Ap/Bp stars are referred to as CVn variables.
Most ATLAS UCBH stars are therefore CVn stars, although only a
minority of CVn stars in the literature have UCBH light curves. The
fact that CVn stars dominate the UCBH class suggests that lone
bright spots with sufficient size and contrast develop more readily on Ap/Bp
stars than on any other type. The CVn UCBH stars may be
characterized by a specific magnetic field topology, making them intriguing
targets for future Zeeman-Doppler imaging.Comment: 18 pages, 8 figures, accepted to A
The FSVS Cluster Catalogue: Galaxy Clusters and Groups in the Faint Sky Variability Survey
We describe a large sample of 598 galaxy clusters and rich groups discovered
in the data of the Faint Sky Variability Survey. The clusters have been
identified using a fully automated, semi-parametric technique based on a
maximum likelihood approach applied to Voronoi tessellation, and enhanced by
colour discrimination. The sample covers a wide range of richness, has a
density of ~28 clusters per sqdeg, and spans a range of estimated redshifts of
0.05 = 0.345. Assuming the presence of a cluster red
sequence, the uncertainty of the estimated cluster redshifts is assessed to be
\~0.03. Containing over 100 clusters with z > 0.6, the catalogue contributes
substantially to the current total of optically-selected, intermediate-redshift
clusters, and complements the existing, usually X-ray selected, samples. The
FSVS fields are accessible for observation throughout the whole year, making
them particularly suited for large follow-up programmes. The construction of
this FSVS Cluster Catalogue completes a fundamental component of our continuing
programmes to investigate the environments of quasars and the chemical
evolution of galaxies. We publish here the list of all clusters with their
basic parameters, and discuss some illustrative examples in more detail. The
full FSVS Cluster Catalogue, together with images and lists of member galaxies
etc., will be issued as part of the ``NOAO data products'', and accessible at
http://www.noao.edu/dpp/. We describe the format of these data and access to
them.Comment: 19 pages and 17 figures, MNRAS accepte
Recommended from our members
Gait Adaptation to Asymmetric Hip Stiffness Applied by a Robotic Exoskeleton
Wearable exoskeletons show significant potential for improving gait impairments, such as interlimb asymmetry. However, a more profound understanding of whether exoskeletons are capable of eliciting neural adaptation is needed. This study aimed to characterize how individuals adapt to bilateral asymmetric joint stiffness applied by a hip exoskeleton, similar to split-belt treadmill training. Thirteen unimpaired individuals performed a walking trial on the treadmill while wearing the exoskeleton. The right side of the exoskeleton acted as a positive stiffness torsional spring, pulling the thigh towards the neutral standing position, while the left acted as a negative stiffness spring pulling the thigh away from the neutral standing position. The results showed that this intervention applied by a hip exoskeleton elicited adaptation in spatiotemporal and kinetic gait measures similar to split-belt treadmill training. These results demonstrate the potential of the proposed intervention for retraining symmetric gait
An EUV Study of the Intermediate Polar EX Hydrae
On 2000 May 5, we began a large multi-wavelength campaign to study the
intermediate polar, EX Hydrae. The simultaneous observations from six
satellites and four telescopes were centered around a one million second
observation with EUVE. Although EX Hydrae has been studied previously with
EUVE, our higher signal-to-noise observations present new results and challenge
the current IP models. Previously unseen dips in the light curve are
reminiscent of the stream dips seen in polar light curves. Also of interest is
the temporal extent of the bulge dip; approximately 0.5 in phase, implying that
the bulge extends over half of the accretion disk. We propose that the magnetic
field in EX Hydrae is strong enough (a few MG) to begin pulling material
directly from the outer edge of the disk, thereby forming a large accretion
curtain which would produce a very broad bulge dip. This would also result in
magnetically controlled accretion streams originating from the outer edge of
the disk. We also present a period analysis of the photometric data which shows
numerous beat frequencies with strong power and also intermittent and wandering
frequencies, an indication that physical conditions within EX Hya changed over
the course of the observation. Iron spectral line ratios give a temperature of
log T=6.5-6.9 K for all spin phases and a poorly constrained density of
n_e=10^10-10^11 cm^-3 for the emitting plasma. This paper is the first in a
series detailing our results from this multi-wavelength observational campaign.Comment: 27 pages, 7 figures, accepted for publication in Ap
Force distributions in a triangular lattice of rigid bars
We study the uniformly weighted ensemble of force balanced configurations on
a triangular network of nontensile contact forces. For periodic boundary
conditions corresponding to isotropic compressive stress, we find that the
probability distribution for single-contact forces decays faster than
exponentially. This super-exponential decay persists in lattices diluted to the
rigidity percolation threshold. On the other hand, for anisotropic imposed
stresses, a broader tail emerges in the force distribution, becoming a pure
exponential in the limit of infinite lattice size and infinitely strong
anisotropy.Comment: 11 pages, 17 figures Minor text revisions; added references and
acknowledgmen
A coupled terrestrial and aquatic biogeophysical model of the Upper Merrimack River watershed, New Hampshire, to inform ecosystem services evaluation and management under climate and land-cover change
Accurate quantification of ecosystem services (ES) at regional scales is increasingly important for making informed decisions in the face of environmental change. We linked terrestrial and aquatic ecosystem process models to simulate the spatial and temporal distribution of hydrological and water quality characteristics related to ecosystem services. The linked model integrates two existing models (a forest ecosystem model and a river network model) to establish consistent responses to changing drivers across climate, terrestrial, and aquatic domains. The linked model is spatially distributed, accounts for terrestrial–aquatic and upstream–downstream linkages, and operates on a daily time-step, all characteristics needed to understand regional responses. The model was applied to the diverse landscapes of the Upper Merrimack River watershed, New Hampshire, USA. Potential changes in future environmental functions were evaluated using statistically downscaled global climate model simulations (both a high and low emission scenario) coupled with scenarios of changing land cover (centralized vs. dispersed land development) for the time period of 1980–2099. Projections of climate, land cover, and water quality were translated into a suite of environmental indicators that represent conditions relevant to important ecosystem services and were designed to be readily understood by the public. Model projections show that climate will have a greater influence on future aquatic ecosystem services (flooding, drinking water, fish habitat, and nitrogen export) than plausible changes in land cover. Minimal changes in aquatic environmental indicators are predicted through 2050, after which the high emissions scenarios show intensifying impacts. The spatially distributed modeling approach indicates that heavily populated portions of the watershed will show the strongest responses. Management of land cover could attenuate some of the changes associated with climate change and should be considered in future planning for the region
Toward Fulfilling the Promise of Molecular Medicine in Fragile X
Fragile X syndrome (FXS) is the most common inherited form of mental retardation and a leading known cause of autism. It is caused by loss of expression of the fragile X mental retardation protein (FMRP), an RNA-binding protein that negatively regulates protein synthesis. In neurons, multiple lines of evidence suggest that protein synthesis at synapses is triggered by activation of group 1 metabotropic glutamate receptors (Gp1 mGluRs) and that many functional consequences of activating these receptors are altered in the absence of FMRP. These observations have led to the theory that exaggerated protein synthesis downstream of Gp1 mGluRs is a core pathogenic mechanism in FXS. This excess can be corrected by reducing signaling by Gp1 mGluRs, and numerous studies have shown that inhibition of mGluR5, in particular, can ameliorate multiple mutant phenotypes in animal models of FXS. Clinical trials based on this therapeutic strategy are currently under way. FXS is therefore poised to be the first neurobehavioral disorder in which corrective treatments have been developed from the bottom up: from gene identification to pathophysiology in animals to novel therapeutics in humans. The insights gained from FXS and other autism-related single-gene disorders may also assist in identifying molecular mechanisms and potential treatment approaches for idiopathic autism.Eunice Kennedy Shriver National Institute of Child Health and Human Development (U.S.)National Institute of Mental Health (U.S.)FRAXA Research Foundatio
- …