1,223 research outputs found
How to Find More Supernovae with Less Work: Object Classification Techniques for Difference Imaging
We present the results of applying new object classification techniques to
difference images in the context of the Nearby Supernova Factory supernova
search. Most current supernova searches subtract reference images from new
images, identify objects in these difference images, and apply simple threshold
cuts on parameters such as statistical significance, shape, and motion to
reject objects such as cosmic rays, asteroids, and subtraction artifacts.
Although most static objects subtract cleanly, even a very low false positive
detection rate can lead to hundreds of non-supernova candidates which must be
vetted by human inspection before triggering additional followup. In comparison
to simple threshold cuts, more sophisticated methods such as Boosted Decision
Trees, Random Forests, and Support Vector Machines provide dramatically better
object discrimination. At the Nearby Supernova Factory, we reduced the number
of non-supernova candidates by a factor of 10 while increasing our supernova
identification efficiency. Methods such as these will be crucial for
maintaining a reasonable false positive rate in the automated transient alert
pipelines of upcoming projects such as PanSTARRS and LSST.Comment: 25 pages; 6 figures; submitted to Ap
Using visual analytics to develop situation awareness in astrophysics
We present a novel collaborative visual analytics application for cognitively overloaded users in the astrophysics domain. The system was developed for scientists who need to analyze heterogeneous, complex data under time pressure, and make predictions and time-critical decisions rapidly and correctly under a constant influx of changing data. The Sunfall Data Taking system utilizes several novel visualization and analysis techniques to enable a team of geographically distributed domain specialists to effectively and remotely maneuver a custom-built instrument under challenging operational conditions. Sunfall Data Taking has been in production use for 2 years by a major international astrophysics collaboration (the largest data volume supernova search currently in operation), and has substantially improved the operational efficiency of its users. We describe the system design process by an interdisciplinary team, the system architecture and the results of an informal usability evaluation of the production system by domain experts in the context of Endsley's three levels of situation awareness
Extremely Red Objects in the Field of QSO 1213-0017: A Galaxy Concentration at z=1.31
We have discovered a concentration of extremely red objects (EROs; R-K>6) in
the field of the z=2.69 quasar QSO 1213-0017 (UM 485), which is significantly
overabundant compared to the field ERO surface density. The optical/near-IR
colors of the EROs and numerous other red galaxies in this field are consistent
with elliptical galaxies at z=1-2. HST optical images for a subset of galaxies
show regular morphologies, most of them being disky or diffuse and without any
obvious evidence for interactions. Ground-based IR images show similar
morphologies, indicating any dust reddening in these objects is spatially
uniform. Optical spectroscopy with the W. M. Keck Telescope has found that four
of the red galaxies lie at =1.31, and a fifth lies in the foreground at
z=1.20. Of the =1.31 galaxies, one is a reddened AGN while the remaining
three have rest-frame UV absorption-line spectra characteristic of old (few
Gyr) stellar populations, similar to the old red galaxy LBDS 53W091 at z=1.55.
Including the MgII absorber seen in the QSO spectrum, we find five galaxies at
=1.31 spread over 1.5 h_50^{-1} Mpc on the sky. These results suggest we
have discovered a coherent structure of old galaxies at high-redshift, possibly
associated with a massive galaxy cluster.Comment: 37 pages including 11 Postscript figures. To appear in the June 2000
issue of the Astronomical Journa
Initial Hubble Diagram Results from the Nearby Supernova Factory
The use of Type Ia supernovae as distance indicators led to the discovery of
the accelerating expansion of the universe a decade ago. Now that large second
generation surveys have significantly increased the size and quality of the
high-redshift sample, the cosmological constraints are limited by the currently
available sample of ~50 cosmologically useful nearby supernovae. The Nearby
Supernova Factory addresses this problem by discovering nearby supernovae and
observing their spectrophotometric time development. Our data sample includes
over 2400 spectra from spectral timeseries of 185 supernovae. This talk
presents results from a portion of this sample including a Hubble diagram
(relative distance vs. redshift) and a description of some analyses using this
rich dataset.Comment: Short version of proceedings for ICHEP08, Philadelphia PA, July 2008;
see v1 for full-length versio
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Sunfall: a collaborative visual analytics system for astrophysics
Computational and experimental sciences produce and collect ever-larger and complex datasets, often in large-scale, multi-institution projects. The inability to gain insight into complex scientific phenomena using current software tools is a bottleneck facing virtually all endeavors of science. In this paper, we introduce Sunfall, a collaborative visual analytics system developed for the Nearby Supernova Factory, an international astrophysics experiment and the largest data volume supernova search currently in operation. Sunfall utilizes novel interactive visualization and analysis techniques to facilitate deeper scientific insight into complex, noisy, high-dimensional, high-volume, time-critical data. The system combines novel image processing algorithms, statistical analysis, and machine learning with highly interactive visual interfaces to enable collaborative, user-driven scientific exploration of supernova image and spectral data. Sunfall is currently in operation at the Nearby Supernova Factory; it is the first visual analytics system in production use at a major astrophysics project
Observing the build-up of the colour-magnitude relation at redshift ~0.8
We analyse the rest-frame (U-V) colour-magnitude relation for 2 clusters at
redshift 0.7 and 0.8, drawn from the ESO Distant Cluster Survey. By comparing
with the population of red galaxies in the Coma cluster, we show that the high
redshift clusters exhibit a deficit of passive faint red galaxies. Our results
show that the red-sequence population cannot be explained in terms of a
monolithic and synchronous formation scenario. A large fraction of faint
passive galaxies in clusters today has moved onto the red sequence relatively
recently as a consequence of the fact that their star formation activity has
come to an end at z<0.8.Comment: 5 pages, 2 figures, to appear in Proc. of IAU Colloq. 195: "Outskirts
of Galaxy Clusters: Intense Life in the Suburbs" -- minor typos correcte
Concordance between chest X ray (CXR) and point of care ultrasound (POCUS) findings in children diagnosed with RSV infection by nasopharyngeal RT-PCR: the Zambia experience
NIHhttp://www.cs.bu.edu/faculty/betke/papers/Camelo-et-alRSV-POCUS-vs-CXR-Poster.pdfAccepted manuscrip
Cooling Flow Star Formation and the Apparent Stellar Ages of Elliptical Galaxies
Observational constraints and theoretical arguments indicate that cooled
interstellar gas in bright elliptical galaxies forms into a young stellar
population throughout the region within the half-light radius. The young
population has a bottom-heavy, but optically luminous IMF extending to 1 - 2
M_sun. When the colors and spectral features of this young population are
combined with those of the underlying old stellar population, the apparent ages
are significantly reduced, similar to the relatively young apparent ages
observed in many ellipticals. Galactic mergers are not required to resupply
young stars. The sensitivity of continuous star formation to L_B and L_x/L_B is
likely to account for the observed spread in apparent ages among elliptical
galaxies. Local star formation is accompanied by enhanced stellar H_beta
equivalent widths, stronger optical emission lines, enhanced thermal X-ray
emission and lower apparent temperatures in the hot gas. The young stars should
cause M/L to vary with galactic radius, perturbing the fundamental plane
occupied by the old stars.Comment: 6 pages with 2 figures; accepted by Astrophysical Journal Letter
The Morphological Content of Ten EDisCS Clusters at 0.5 < z < 0.8
We describe Hubble Space Telescope (HST) imaging of 10 of the 20 ESO Distant
Cluster Survey (EDisCS) fields. Each ~40 square arcminute field was imaged in
the F814W filter with the Advanced Camera for Surveys Wide Field Camera. Based
on these data, we present visual morphological classifications for the ~920
sources per field that are brighter than I_auto=23 mag. We use these
classifications to quantify the morphological content of 10
intermediate-redshift (0.5 < z < 0.8) galaxy clusters within the HST survey
region. The EDisCS results, combined with previously published data from seven
higher redshift clusters, show no statistically significant evidence for
evolution in the mean fractions of elliptical, S0, and late-type (Sp+Irr)
galaxies in clusters over the redshift range 0.5 < z < 1.2. In contrast,
existing studies of lower redshift clusters have revealed a factor of ~2
increase in the typical S0 fraction between z=0.4 and z=0, accompanied by a
commensurate decrease in the Sp+Irr fraction and no evolution in the elliptical
fraction. The EDisCS clusters demonstrate that cluster morphological fractions
plateau beyond z ~ 0.4. They also exhibit a mild correlation between
morphological content and cluster velocity dispersion, highlighting the
importance of careful sample selection in evaluating evolution. We discuss
these findings in the context of a recently proposed scenario in which the
fractions of passive (E,S0) and star-forming (Sp,Irr) galaxies are determined
primarily by the growth history of clusters.Comment: 18 pages, 7 figures; To be published in ApJ; minor changes made to
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