2,257 research outputs found
Fatty infiltration of the cervical multifidus musculature and their clinical correlates in spondylotic myelopathy.
This work was supported by the National Institute of Health, National Institute of Neurological Disorders and Stroke (US), (NIH-NINDS), grant number 1K23NS091430-01A1Peer reviewe
Planet Hunters VII. Discovery of a New Low-Mass, Low-Density Planet (PH3 c) Orbiting Kepler-289 with Mass Measurements of Two Additional Planets (PH3 b and d)
We report the discovery of one newly confirmed planet ( days,
) and mass determinations of two previously
validated Kepler planets, Kepler-289 b ( days,
) and Kepler-289-c ( days,
), through their transit timing variations
(TTVs). We also exclude the possibility that these three planets reside in a
Laplace resonance. The outer planet has very deep (), high
signal-to-noise transits, which puts extremely tight constraints on its host
star's stellar properties via Kepler's Third Law. The star PH3 is a young
( Gyr as determined by isochrones and gyrochronology), Sun-like star
with , , and
K. The middle planet's large TTV amplitude (
hours) resulted either in non-detections or inaccurate detections in previous
searches. A strong chopping signal, a shorter period sinusoid in the TTVs,
allows us to break the mass-eccentricity degeneracy and uniquely determine the
masses of the inner, middle, and outer planets to be ,
, and , which we designate PH3 b, c, and
d, respectively. Furthermore, the middle planet, PH3 c, has a relatively low
density, g/cm for a planet of its mass, requiring a
substantial H/He atmosphere of by mass, and joins a
growing population of low-mass, low-density planets.Comment: 21 pages, 10 figures, 5 tables, accepted into Ap
Space Warps II. New Gravitational Lens Candidates from the CFHTLS Discovered through Citizen Science
We report the discovery of 29 promising (and 59 total) new lens candidates
from the CFHT Legacy Survey (CFHTLS) based on about 11 million classifications
performed by citizen scientists as part of the first Space Warps lens search.
The goal of the blind lens search was to identify lens candidates missed by
robots (the RingFinder on galaxy scales and ArcFinder on group/cluster scales)
which had been previously used to mine the CFHTLS for lenses. We compare some
properties of the samples detected by these algorithms to the Space Warps
sample and find them to be broadly similar. The image separation distribution
calculated from the Space Warps sample shows that previous constraints on the
average density profile of lens galaxies are robust. SpaceWarps recovers about
65% of known lenses, while the new candidates show a richer variety compared to
those found by the two robots. This detection rate could be increased to 80% by
only using classifications performed by expert volunteers (albeit at the cost
of a lower purity), indicating that the training and performance calibration of
the citizen scientists is very important for the success of Space Warps. In
this work we present the SIMCT pipeline, used for generating in situ a sample
of realistic simulated lensed images. This training sample, along with the
false positives identified during the search, has a legacy value for testing
future lens finding algorithms. We make the pipeline and the training set
publicly available.Comment: 23 pages, 12 figures, MNRAS accepted, minor to moderate changes in
this versio
Planet Hunters. V. A Confirmed Jupiter-Size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data
We report the latest Planet Hunter results, including PH2 b, a Jupiter-size
(R_PL = 10.12 \pm 0.56 R_E) planet orbiting in the habitable zone of a
solar-type star. PH2 b was elevated from candidate status when a series of
false positive tests yielded a 99.9% confidence level that transit events
detected around the star KIC 12735740 had a planetary origin. Planet Hunter
volunteers have also discovered 42 new planet candidates in the Kepler public
archive data, of which 33 have at least three transits recorded. Most of these
transit candidates have orbital periods longer than 100 days and 20 are
potentially located in the habitable zones of their host stars. Nine candidates
were detected with only two transit events and the prospective periods are
longer than 400 days. The photometric models suggest that these objects have
radii that range between Neptune to Jupiter. These detections nearly double the
number of gas giant planet candidates orbiting at habitable zone distances. We
conducted spectroscopic observations for nine of the brighter targets to
improve the stellar parameters and we obtained adaptive optics imaging for four
of the stars to search for blended background or foreground stars that could
confuse our photometric modeling. We present an iterative analysis method to
derive the stellar and planet properties and uncertainties by combining the
available spectroscopic parameters, stellar evolution models, and transiting
light curve parameters, weighted by the measurement errors. Planet Hunters is a
citizen science project that crowd-sources the assessment of NASA Kepler light
curves. The discovery of these 43 planet candidates demonstrates the success of
citizen scientists at identifying planet candidates, even in longer period
orbits with only two or three transit events.Comment: 35 pages, 11 figures, 6 tables, accepted and published on ApJ ApJ,
776, 1
Linking goniometer measurements to hyperspectral and multi-sensor imagery for retrieval of beach properties and coastal characterization
In June 2011, a multi-sensor airborne remote sensing campaign was flown at the Virginia Coast Reserve Long Term Ecological Research site with coordinated ground and water calibration and validation (cal/val) measurements. Remote sensing imagery acquired during the ten day exercise included hyperspectral imagery (CASI-1500), topographic LiDAR, and thermal infra-red imagery, all simultaneously from the same aircraft. Airborne synthetic aperture radar (SAR) data acquisition for a smaller subset of sites occurred in September 2011 (VCR\u2711). Focus areas for VCR\u2711 were properties of beaches and tidal flats and barrier island vegetation and, in the water column, shallow water bathymetry. On land, cal/val emphasized tidal flat and beach grain size distributions, density, moisture content, and other geotechnical properties such as shear and bearing strength (dynamic deflection modulus), which were related to hyperspectral BRDF measurements taken with the new NRL Goniometer for Outdoor Portable Hyperspectral Earth Reflectance (GOPHER). This builds on our earlier work at this site in 2007 related to beach properties and shallow water bathymetry. A priority for VCR\u2711 was to collect and model relationships between hyperspectral imagery, acquired from the aircraft at a variety of different phase angles, and geotechnical properties of beaches and tidal flats. One aspect of this effort was a demonstration that sand density differences are observable and consistent in reflectance spectra from GOPHER data, in CASI hyperspectral imagery, as well as in hyperspectral goniometer measurements conducted in our laboratory after VCR\u2711
Galaxy Zoo: Mergers ā Dynamical models of interacting galaxies
The dynamical history of most merging galaxies is not well understood. Correlations between galaxy interaction and star formation have been found in previous studies, but require the context of the physical history of merging systems for full insight into the processes that lead to enhanced star formation. We present the results of simulations that reconstruct the orbit trajectories and disturbed morphologies of pairs of interacting galaxies. With the use of a restricted three-body simulation code and the help of citizen scientists, we sample 105 points in parameter space for each system. We demonstrate a successful recreation of the morphologies of 62 pairs of interacting galaxies through the review of more than 3 million simulations. We examine the level of convergence and uniqueness of the dynamical properties of each system. These simulations represent the largest collection of models of interacting galaxies to date, providing a valuable resource for the investigation of mergers. This paper presents the simulation parameters generated by the project. They are now publicly available in electronic format at http://data.galaxyzoo.org/mergers.html. Though our best-fitting model parameters are not an exact match to previously published models, our method for determining uncertainty measurements will aid future comparisons between models. The dynamical clocks from our models agree with previous results of the time since the onset of star formation from starburst models in interacting systems and suggest that tidally induced star formation is triggered very soon after closest approach
A deep Chandra observation of the poor cluster AWM 4 - I. Properties of the central radio galaxy and its effects on the intracluster medium
Using observations from the Chandra X-ray Observatory and Giant Metrewave
Radio Telescope, we examine the interaction between the intracluster medium and
central radio source in the poor cluster AWM 4. In the Chandra observation a
small cool core or galactic corona is resolved coincident with the radio core.
This corona is capable of fuelling the active nucleus, but must be
inefficiently heated by jet interactions or conduction, possibly precluding a
feedback relationship between the radio source and cluster. A lack of clearly
detected X-ray cavities suggests that the radio lobes are only partially filled
by relativistic plasma. We estimate a filling factor of phi=0.21 (3 sigma upper
limit phi<0.42) for the better constrained east lobe. We consider the particle
population in the jets and lobes, and find that the standard equipartition
assumptions predict pressures and ages which agree poorly with X-ray estimates.
Including an electron population extending to low Lorentz factors either
reduces (gamma_min=100) or removes (gamma_min=10) the pressure imbalance
between the lobes and their environment. Pressure balance can also be achieved
by entrainment of thermal gas, probably in the first few kiloparsecs of the
radio jets. We estimate the mechanical power output of the radio galaxy, and
find it to be marginally capable of balancing radiative cooling.Comment: Accepted for publication in MNRAS, 18 pages, 9 postscript figures
Space Warps: I. Crowd-sourcing the Discovery of Gravitational Lenses
We describe Space Warps, a novel gravitational lens discovery service that
yields samples of high purity and completeness through crowd-sourced visual
inspection. Carefully produced colour composite images are displayed to
volunteers via a web- based classification interface, which records their
estimates of the positions of candidate lensed features. Images of simulated
lenses, as well as real images which lack lenses, are inserted into the image
stream at random intervals; this training set is used to give the volunteers
instantaneous feedback on their performance, as well as to calibrate a model of
the system that provides dynamical updates to the probability that a classified
image contains a lens. Low probability systems are retired from the site
periodically, concentrating the sample towards a set of lens candidates. Having
divided 160 square degrees of Canada-France-Hawaii Telescope Legacy Survey
(CFHTLS) imaging into some 430,000 overlapping 82 by 82 arcsecond tiles and
displaying them on the site, we were joined by around 37,000 volunteers who
contributed 11 million image classifications over the course of 8 months. This
Stage 1 search reduced the sample to 3381 images containing candidates; these
were then refined in Stage 2 to yield a sample that we expect to be over 90%
complete and 30% pure, based on our analysis of the volunteers performance on
training images. We comment on the scalability of the SpaceWarps system to the
wide field survey era, based on our projection that searches of 10 images
could be performed by a crowd of 10 volunteers in 6 days.Comment: 21 pages, 13 figures, MNRAS accepted, minor to moderate changes in
this versio
Planet Hunters: Assessing the Kepler Inventory of Short Period Planets
We present the results from a search of data from the first 33.5 days of the
Kepler science mission (Quarter 1) for exoplanet transits by the Planet Hunters
citizen science project. Planet Hunters enlists members of the general public
to visually identify transits in the publicly released Kepler light curves via
the World Wide Web. Over 24,000 volunteers reviewed the Kepler Quarter 1 data
set. We examine the abundance of \geq 2 R\oplus planets on short period (< 15
days) orbits based on Planet Hunters detections. We present these results along
with an analysis of the detection efficiency of human classifiers to identify
planetary transits including a comparison to the Kepler inventory of planet
candidates. Although performance drops rapidly for smaller radii, \geq 4
R\oplus Planet Hunters \geq 85% efficient at identifying transit signals for
planets with periods less than 15 days for the Kepler sample of target stars.
Our high efficiency rate for simulated transits along with recovery of the
majority of Kepler \geq 4 R\oplus planets suggest suggests the Kepler inventory
of \geq 4 R\oplus short period planets is nearly complete.Comment: 41 pages,13 figures, 8 tables, accepted to Ap
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