1,119 research outputs found
Dark energy and curvature from a future baryonic acoustic oscillation survey using the Lyman-alpha forest
We explore the requirements for a Lyman-alpha forest (LyaF) survey designed
to measure the angular diameter distance and Hubble parameter at 2~<z~<4 using
the standard ruler provided by baryonic acoustic oscillations (BAO). The goal
would be to obtain a high enough density of sources to probe the
three-dimensional density field on the scale of the BAO feature. A
percent-level measurement in this redshift range can almost double the Dark
Energy Task Force Figure of Merit, relative to the case with only a similar
precision measurement at z~1, if the Universe is not assumed to be flat. This
improvement is greater than the one obtained by doubling the size of the z~1
survey, with Planck and a weak SDSS-like z=0.3 BAO measurement assumed in each
case. Galaxy BAO surveys at z~1 may be able to make an effective LyaF
measurement simultaneously at minimal added cost, because the required number
density of quasars is relatively small. We discuss the constraining power as a
function of area, magnitude limit (density of quasars), resolution, and
signal-to-noise of the spectra. For example, a survey covering 2000 sq. deg.
and achieving S/N=1.8 per Ang. at g=23 (~40 quasars per sq. deg.) with an
R~>250 spectrograph is sufficient to measure both the radial and transverse
oscillation scales to 1.4% from the LyaF (or better, if fainter magnitudes and
possibly Lyman-break galaxies can be used). At fixed integration time and in
the sky-noise-dominated limit, a wider, noisier survey is generally more
efficient; the only fundamental upper limit on noise being the need to identify
a quasar and find a redshift. Because the LyaF is much closer to linear and
generally better understood than galaxies, systematic errors are even less
likely to be a problem.Comment: 18 pages including 6 figures, submitted to PR
Expected Large Synoptic Survey Telescope (LSST) Yield of Eclipsing Binary Stars
In this paper we estimate the Large Synoptic Survey Telescope (LSST) yield of
eclipsing binary stars, which will survey ~20,000 square degrees of the
southern sky during the period of 10 years in 6 photometric passbands to r ~
24.5. We generate a set of 10,000 eclipsing binary light curves sampled to the
LSST time cadence across the whole sky, with added noise as a function of
apparent magnitude. This set is passed to the Analysis of Variance (AoV) period
finder to assess the recoverability rate for the periods, and the successfully
phased light curves are passed to the artificial intelligence-based pipeline
EBAI to assess the recoverability rate in terms of the eclipsing binaries'
physical and geometric parameters. We find that, out of ~24 million eclipsing
binaries observed by LSST with S/N>10 in mission life-time, ~28% or 6.7 million
can be fully characterized by the pipeline. Of those, ~25% or 1.7 million will
be double-lined binaries, a true treasure trove for stellar astrophysics.Comment: 19 pages, 7 figures. Accepted to AJ, to appear in issue 142:2 (Aug
2011
Power spectrum of the maxBCG sample: detection of acoustic oscillations using galaxy clusters
We use the direct Fourier method to calculate the redshift-space power
spectrum of the maxBCG cluster catalog -- currently by far the largest existing
galaxy cluster sample. The total number of clusters used in our analysis is
12,616. After accounting for the radial smearing effect caused by photometric
redshift errors and also introducing a simple treatment for the nonlinear
effects, we show that currently favored low matter density "concordance" LCDM
cosmology provides a very good fit to the estimated power. Thanks to the large
volume (~0.4 h^{-3}Gpc^{3}), high clustering amplitude (linear effective bias
parameter b_{eff} ~3x(0.85/sigma_8)), and sufficiently high sampling density
(~3x10^{-5} h^{3}Mpc^{-3}) the recovered power spectrum has high enough signal
to noise to allow us to find evidence (~2 sigma CL) for the baryonic acoustic
oscillations (BAO). In case the clusters are additionally weighted by their
richness the resulting power spectrum has slightly higher large-scale amplitude
and smaller damping on small scales. As a result the confidence level for the
BAO detection is somewhat increased: ~2.5 sigma. The ability to detect BAO with
relatively small number of clusters is encouraging in the light of several
proposed large cluster surveys.Comment: MNRAS accepted, extended analysis of arXiv:0705.1843, 15 page
The rapidly pulsating sdO star, SDSS J160043.6+074802.9
A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system
containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields
Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely
type of K3V for the secondary star. We compare our results with atmospheric
parameters derived by Fontaine et al. (2008) and in the context of existing
evolution models for sdO stars. New and more extensive photometry is also
presented which recovers most, but not all, frequencies found in an earlier
paper. It therefore seems probable that some pulsation modes have variable
amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO
models show those having log g > 5.3 to be more likely to be unstable and
capable of driving pulsation in the observed frequency range.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 2009
September
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Inspection and evaluation of artifacts in digital video sources
Streaming digital video content providers such as YouTube, Amazon, Hulu, and Netflix collaborate with production teams to obtain new and old video content. These collaborations lead to an accumulation of video sources, some of which might contain unacceptable visual artifacts. Artifacts may inadvertently enter the video master at any point in the production pipeline, due to any of a number of equipment and user failures. Unfortunately, these artifacts are difficult to detect since no pristine reference exists for comparison. As of now, few automated tools exist that can effectively capture the most common forms of these artifacts. This work studies no-reference video source inspection for generalized artifact detection and subjective quality prediction, which will ultimate inform decisions related to acquisition of new content.
Automatically identifying the locations and severities of video artifacts is a difficult problem. We have developed a general method for detecting local artifacts by learning differences in the statistics between distorted and pristine video frames. Our model, which we call the Video Impairment Mapper (VID-MAP), produces a full resolution map of artifact detection probabilities based on comparisons of excitatory and inhibatory convolutional responses. Validation on a large database shows that our method outperforms the previous state-of-the-art of even distortion-specific detectors.
A variety of powerful picture quality predictors are available that rely on neuro-statistical models of distortion perception. We extend these principles to video source inspection, by coupling spatial divisive normalization with a series of filterbanks tuned for artifact detection, implemented using a common convolutional framework. We developed the Video Impairment Detection by SParse Error CapTure (VIDSPECT) model, which leverages discriminative sparse dictionaries that are tuned to detect specific artifacts. VIDSPECT is simple, highly generalizable, and yields better accuracy than competing methods.
To evaluate the perceived quality of video sources containing artifacts, we built a new digital video database, called the LIVE Video Masters Database, which contains 384 videos affected by the types of artifacts encountered in otherwise pristine digital video sources. We find that VIDSPECT delivers top performance on this database for most artifacts tested, and competitive performance otherwise, using the same basic architecture in all cases.Electrical and Computer Engineerin
The Rotation of M Dwarfs Observed by the Apache Point Galactic Evolution Experiment
We present the results of a spectroscopic analysis of rotational velocities
in 714 M dwarf stars observed by the SDSS III Apache Point Galactic Evolution
Experiment (APOGEE) survey. We use a template fitting technique to estimate
while simultaneously estimating , ,
and . We conservatively estimate that our detection limit is 8
km s. We compare our results to M dwarf rotation studies in the
literature based on both spectroscopic and photometric measurements. Like other
authors, we find an increase in the fraction of rapid rotators with decreasing
stellar temperature, exemplified by a sharp increase in rotation near the M
transition to fully convective stellar interiors, which is consistent with the
hypothesis that fully convective stars are unable to shed angular momentum as
efficiently as those with radiative cores. We compare a sample of targets
observed both by APOGEE and the MEarth transiting planet survey and find no
cases were the measured and rotation period are physically
inconsistent, requiring . We compare our spectroscopic results to
the fraction of rotators inferred from photometric surveys and find that while
the results are broadly consistent, the photometric surveys exhibit a smaller
fraction of rotators beyond the M transition by a factor of . We
discuss possible reasons for this discrepancy. Given our detection limit, our
results are consistent with a bi-modal distribution in rotation that is seen in
photometric surveys.Comment: 31 pages, 11 figures, 4 tables. Accepted for publication by A
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