336 research outputs found
Full-depth Coadds of the WISE and First-year NEOWISE-Reactivation Images
The Near Earth Object Wide-field Infrared Survey Explorer (NEOWISE)
Reactivation mission released data from its first full year of observations in
2015. This data set includes ~2.5 million exposures in each of W1 and W2,
effectively doubling the amount of WISE imaging available at 3.4 and 4.6
microns relative to the AllWISE release. We have created the first ever
full-sky set of coadds combining all publicly available W1 and W2 exposures
from both the AllWISE and NEOWISE-Reactivation (NEOWISER) mission phases. We
employ an adaptation of the unWISE image coaddition framework (Lang 2014),
which preserves the native WISE angular resolution and is optimized for forced
photometry. By incorporating two additional scans of the entire sky, we not
only improve the W1/W2 depths, but also largely eliminate time-dependent
artifacts such as off-axis scattered moonlight. We anticipate that our new
coadds will have a broad range of applications, including target selection for
upcoming spectroscopic cosmology surveys, identification of distant/massive
galaxy clusters, and discovery of high-redshift quasars. In particular, our
full-depth AllWISE+NEOWISER coadds will be an important input for the Dark
Energy Spectroscopic Instrument (DESI) selection of luminous red galaxy and
quasar targets. Our full-depth W1/W2 coadds are already in use within the DECam
Legacy Survey (DECaLS) and Mayall z-band Legacy Survey (MzLS) reduction
pipelines. Much more work still remains in order to fully leverage NEOWISER
imaging for astrophysical applications beyond the solar system.Comment: coadds available at http://unwise.me, zoomable full-sky rendering at
http://legacysurvey.org/viewe
Astrometry.net: Blind astrometric calibration of arbitrary astronomical images
We have built a reliable and robust system that takes as input an
astronomical image, and returns as output the pointing, scale, and orientation
of that image (the astrometric calibration or WCS information). The system
requires no first guess, and works with the information in the image pixels
alone; that is, the problem is a generalization of the "lost in space" problem
in which nothing--not even the image scale--is known. After robust source
detection is performed in the input image, asterisms (sets of four or five
stars) are geometrically hashed and compared to pre-indexed hashes to generate
hypotheses about the astrometric calibration. A hypothesis is only accepted as
true if it passes a Bayesian decision theory test against a background
hypothesis. With indices built from the USNO-B Catalog and designed for
uniformity of coverage and redundancy, the success rate is 99.9% for
contemporary near-ultraviolet and visual imaging survey data, with no false
positives. The failure rate is consistent with the incompleteness of the USNO-B
Catalog; augmentation with indices built from the 2MASS Catalog brings the
completeness to 100% with no false positives. We are using this system to
generate consistent and standards-compliant meta-data for digital and digitized
imaging from plate repositories, automated observatories, individual scientific
investigators, and hobbyists. This is the first step in a program of making it
possible to trust calibration meta-data for astronomical data of arbitrary
provenance.Comment: submitted to A
Searching for comets on the World Wide Web: The orbit of 17P/Holmes from the behavior of photographers
We performed an image search for "Comet Holmes," using the Yahoo Web search
engine, on 2010 April 1. Thousands of images were returned. We astrometrically
calibrated---and therefore vetted---the images using the Astrometry.net system.
The calibrated image pointings form a set of data points to which we can fit a
test-particle orbit in the Solar System, marginalizing over image dates and
detecting outliers. The approach is Bayesian and the model is, in essence, a
model of how comet astrophotographers point their instruments. In this work, we
do not measure the position of the comet within each image, but rather use the
celestial position of the whole image to infer the orbit. We find very strong
probabilistic constraints on the orbit, although slightly off the JPL
ephemeris, probably due to limitations of our model. Hyperparameters of the
model constrain the reliability of date meta-data and where in the image
astrophotographers place the comet; we find that ~70 percent of the meta-data
are correct and that the comet typically appears in the central third of the
image footprint. This project demonstrates that discoveries and measurements
can be made using data of extreme heterogeneity and unknown provenance. As the
size and diversity of astronomical data sets continues to grow, approaches like
ours will become more essential. This project also demonstrates that the Web is
an enormous repository of astronomical information; and that if an object has
been given a name and photographed thousands of times by observers who post
their images on the Web, we can (re-)discover it and infer its dynamical
properties.Comment: As published. Changes in v2: data-driven initialization rather than
JPL; added figures; clarified tex
Cleaning the USNO-B Catalog through automatic detection of optical artifacts
The USNO-B Catalog contains spurious entries that are caused by diffraction
spikes and circular reflection halos around bright stars in the original
imaging data. These spurious entries appear in the Catalog as if they were real
stars; they are confusing for some scientific tasks. The spurious entries can
be identified by simple computer vision techniques because they produce
repeatable patterns on the sky. Some techniques employed here are variants of
the Hough transform, one of which is sensitive to (two-dimensional)
overdensities of faint stars in thin right-angle cross patterns centered on
bright (<13 \mag) stars, and one of which is sensitive to thin annular
overdensities centered on very bright (<7 \mag) stars. After enforcing
conservative statistical requirements on spurious-entry identifications, we
find that of the 1,042,618,261 entries in the USNO-B Catalog, 24,148,382 of
them (2.3 \percent) are identified as spurious by diffraction-spike criteria
and 196,133 (0.02 \percent) are identified as spurious by reflection-halo
criteria. The spurious entries are often detected in more than 2 bands and are
not overwhelmingly outliers in any photometric properties; they therefore
cannot be rejected easily on other grounds, i.e., without the use of computer
vision techniques. We demonstrate our method, and return to the community in
electronic form a table of spurious entries in the Catalog.Comment: published in A
Scapular and humeral movement patterns of people with stroke during range-of-motion exercises
BACKGROUND AND PURPOSE: Range-of-motion (ROM) exercises may contribute to hemiparetic shoulder pain, but the underlying mechanisms are unknown. This study examined scapular and humeral movement patterns in people with hemiparesis post stroke as they performed commonly prescribed ROM exercises. METHODS: Using kinematic techniques, we studied 13 people with hemiparesis, both with and without pain, as they performed three commonly prescribed ROM exercises: person-assisted ROM, self-assisted ROM, and cane-assisted ROM. Their data were compared to a group of 12 matched control subjects performing scapular plane shoulder elevation using mixed model ANOVAs. Correlation analyses were used to examine the relationship between participants’ ratings of pain and kinematic data. RESULTS: The hemiparetic group had mild pain at rest that increased during the performance of the exercises. During shoulder elevation, humeral external rotation in the hemiparetic group was decreased in all three ROM exercises compared to the control group. Scapular upward rotation in the hemiparetic group was decreased for the person-assisted ROM exercise only. No differences in scapular tilt were found between groups. The extent of movement abnormalities was not related to pain severity. DISCUSSION AND CONCLUSIONS: People with hemiparesis had altered scapular and humeral movement patterns and increased shoulder pain when performing the ROM exercises. These data can assist clinicians in making decisions regarding which exercises to prescribe to preserve shoulder motion and prevent contractures in this population
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