279,173 research outputs found
Spitzer/IRAC Limits to Planetary Companions of Fomalhaut and epsilon Eridani
Fomalhaut and epsilon Eridani are two young, nearby stars that possess
extended debris disks whose structures suggest the presence of perturbing
planetary objects. With its high sensitivity and stable point spread function,
Spitzer/IRAC is uniquely capable of detecting cool, Jupiter-like planetary
companions whose peak emission is predicted to occur near 4.5 um. We report on
deep IRAC imaging of these two stars, taken at 3.6 and 4.5 um using subarray
mode and in all four channels in wider-field full array mode. Observations
acquired at two different telescope roll angles allowed faint surrounding
objects to be separated from the stellar diffraction pattern. No companion
candidates were detected at the reported position of Fomalhaut b with 3 sigma
model-dependent mass upper limits of 3 MJ (for an age of 200 Myr). Around
epsilon Eridani we instead set a limit of 4 and <1 MJ (1 Gyr model age) at the
inner and outer edge of the sub-millimeter debris ring, respectively. These
results are consistent with non-detections in recent near-infrared imaging
searches, and set the strongest limits to date on the presence of planets
outside epsilon Eridani sub-millimeter ring.Comment: Accepted by The Astrophysical Journal. Request electronic-only plates
to M. Marengo ([email protected]
A Census of Object Types and Redshift Estimates in the SDSS Photometric Catalog from a Trained Decision-Tree Classifier
We have applied ClassX, an oblique decision tree classifier optimized for
astronomical analysis, to the homogeneous multicolor imaging data base of the
Sloan Digital Sky Survey (SDSS), training the software on subsets of SDSS
objects whose nature is precisely known via spectroscopy. We find that the
software, using photometric data only, correctly classifies a very large
fraction of the objects with existing SDSS spectra, both stellar and
extragalactic. ClassX also accurately predicts the redshifts of both normal and
active galaxies in SDSS. To illustrate ClassX applications in SDSS research, we
(a) derive the object content of the SDSS DR2 photometric catalog and (b)
provide a sample catalog of resolved SDSS objects that contains a large number
of candidate AGN galaxies, 27,000, along with 63,000 candidate normal galaxies
at magnitudes substantially fainter than typical magnitudes of SDSS
spectroscopic objects. The surface density of AGN selected by ClassX to i~19 is
in agreement with that quoted by SDSS. When ClassX is applied to the
photometric data fainter than the SDSS spectroscopic limit, the inferred
surface density of AGN rises sharply, as expected. The ability of the
classifier to accurately constrain the redshifts of huge numbers (ultimately ~
10^7) of active galaxies in the photometric data base promises new insights
into fundamental issues of AGN research, such as the evolution of the AGN
luminosity function with cosmic time, the starburst--AGN connection, and
AGN--galactic morphology relationships.Comment: Accepted for publication in The Astronomical Journal, Vol. 130, 2005;
33 pages, 10 figures, 5 tables, AASTeX v5.0. Table 5 will be electronic in
the published journal, but available now at
http://www-int.stsci.edu/~margon/table5.ascii and
http://www-int.stsci.edu/~margon/table5.ascii.g
Polarized light imaging of birefringence and diattenuation at highresolution and high sensitivity
Polarized light microscopy provides unique opportunities for analyzing the
molecular order in man-made and natural materials, including biological
structures inside living cells, tissues, and whole organisms. 20 years ago, the
LC-PolScope was introduced as a modern version of the traditional polarizing
microscope enhanced by liquid crystal devices for the control of polarization,
and by electronic imaging and digital image processing for fast and
comprehensive image acquisition and analysis. The LC- PolScope is commonly used
for birefringence imaging, analyzing the spatial and temporal variations of the
differential phase delay in ordered and transparent materials. Here we describe
an alternative use of the LC-PolScope for imaging the polarization dependent
transmittance of dichroic materials. We explain the minor changes needed to
convert the instrument between the two imaging modes, discuss the relationship
between the quantities measured with either instrument, and touch on the
physical connection between refractive index, birefringence, transmittance,
diattenuation, and dichroism.Comment: 21 pages, 5 figures, accepted for publication in Journal of Optic
Special Section Guest Editorial: Image/Video Quality and System Performance
Rapid developments in display technologies, digital printing, imaging sensors, image processing and image transmission are providing new possibilities for creating and conveying visual content. In an age in which images and video are ubiquitous and where mobile, satellite, and three-dimensional (3-D) imaging have become ordinary experiences, quantification of the performance of modern imaging systems requires appropriate approaches. At the end of the imaging chain, a human observer must decide whether images and video are of a satisfactory visual quality. Hence the measurement and modeling of perceived image quality is of crucial importance, not only in visual arts and commercial applications but also in scientific and entertainment environments. Advances in our understanding of the human visual system offer new possibilities for creating visually superior imaging systems and promise more accurate modeling of image quality. As a result, there is a profusion of new research on imaging performance and perceived quality
Artifact reduction for separable non-local means
It was recently demonstrated [J. Electron. Imaging, 25(2), 2016] that one can
perform fast non-local means (NLM) denoising of one-dimensional signals using a
method called lifting. The cost of lifting is independent of the patch length,
which dramatically reduces the run-time for large patches. Unfortunately, it is
difficult to directly extend lifting for non-local means denoising of images.
To bypass this, the authors proposed a separable approximation in which the
image rows and columns are filtered using lifting. The overall algorithm is
significantly faster than NLM, and the results are comparable in terms of PSNR.
However, the separable processing often produces vertical and horizontal
stripes in the image. This problem was previously addressed by using a
bilateral filter-based post-smoothing, which was effective in removing some of
the stripes. In this letter, we demonstrate that stripes can be mitigated in
the first place simply by involving the neighboring rows (or columns) in the
filtering. In other words, we use a two-dimensional search (similar to NLM),
while still using one-dimensional patches (as in the previous proposal). The
novelty is in the observation that one can use lifting for performing
two-dimensional searches. The proposed approach produces artifact-free images,
whose quality and PSNR are comparable to NLM, while being significantly faster.Comment: To appear in Journal of Electronic Imagin
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