938 research outputs found
A method to resolve the nuclear activity in galaxies, as applied to NGC1358
Nuclear regions of galaxies generally host a mixture of components with
different exitation, composition, and kinematics. Derivation of emission line
ratios and kinematics could then be misleading, if due correction is not made
for the limited spatial and spectral resolutions of the observations. The aim
of this paper is to demonstrate, with application to a long slit spectrum of
the Seyfert2 galaxy NGC1358, how line intensities and velocities, together with
modelling and knowledge of the point spread function, may be used to resolve
the differing structures. In the situation outlined, the observed kinematics
differs for different spectral lines. From the observed intensity and velocity
distributions of a number of spectral lines and with some reasonable
assumptions to diminish the number of free parameters, the true line ratios and
velocity structures may be deduced. A preliminary solution for the nuclear
structure of NGC1358 is obtained, involving a nuclear point source and an
emerging outflow of high excitation with a post shock cloud, as well as a
nuclear emission line disk rotating in the potential of a stellar bulge and
expressing a radial exitation gradient. The method results in a likely scenario
for the nuclear structure of NGC1358. For definitive results an extrapolation
of the method to two dimensions combined with the use of integral field
spectroscopy will generally be necessary.Comment: to appear in proceedings for the IAU 277th Symposium, Editors: C.
Carignan, F. Combes, K. Freema
Calibration of Low-Frequency, Wide-Field Radio Interferometers Using Delay/Delay-Rate Filtering
We present a filtering technique that can be applied to individual baselines
of wide-bandwidth, wide-field interferometric data to geometrically select
regions on the celestial sphere that contain primary calibration sources. The
technique relies on the Fourier transformation of wide-band frequency spectra
from a given baseline to obtain one-dimensional "delay images", and then the
transformation of a time-series of delay images to obtain two-dimensional
"delay/delay-rate images." Source selection is possible in these images given
appropriate combinations of baseline, bandwidth, integration time and source
location. Strong and persistent radio frequency interference (RFI) limits the
effectiveness of this source selection owing to the removal of data by RFI
excision algorithms. A one-dimensional, complex CLEAN algorithm has been
developed to compensate for RFI-excision effects. This approach allows CLEANed,
source-isolated data to be used to isolate bandpass and primary beam gain
functions. These techniques are applied to data from the Precision Array for
Probing the Epoch of Reionization (PAPER) as a demonstration of their value in
calibrating a new generation of low-frequency radio interferometers with wide
relative bandwidths and large fields-of-view.Comment: 17 pages, 6 figures, 2009AJ....138..219
Критичне мислення - перспективний шлях модернизації процесу навчання іноземним мовам студентів немовних факультетів
(uk) У цій статті автор ставить проблему застосування технології критичного мислення для пошуку нових шляхів модернізації процесу навчання іноземним мовам студентів немовних факультетів. Це потрібно для створення інноваційних технологій вивчення іноземних мов в умовах реформування освіти в Україні.(en) The author of the Paper rises the problem of using technology of Critical Thinking fo r searching new ways of modernization of foreign language teaching process fo r students of nonlinguistic departments. It is necessary fo r creating up-to-day innovative technology of foreign languages teaching in conditions of educational reforms
Maximum-likelihood Localization of Overlapping Point Sources in 3D Microscopy Using CLEAN
Precise 3D point localization is increasingly important in microscopy, but algorithms break down when PSFs overlap. We adapt the CLEAN algorithm from astronomical imaging to enable MLE localization of high-density datasets
New 145-MHz Source Measurements by PAPER in the Southern Sky
We present observations from the Precision Array for Probing the Epoch of
Reionization (PAPER) in South Africa, observed in May and September 2010. Using
two nights of drift scanning with PAPER's 60\arcdeg\ FWHM beam we have made a
map covering the entire sky below +10 degrees declination with an effective
center frequency of 145 MHz, a 70-MHz bandwidth, and a resolution of 26\arcmin.
A 4800 square-degree region of this large map with the lowest Galactic emission
reaches an RMS of 0.7 Jy. We establish an absolute flux scale using sources
from the 160-MHz Culgoora catalog. Using the 408-MHz Molonglo Reference Catalog
(MRC) as a finding survey, we identify counterparts to 480 sources in our maps,
and compare our fluxes to the MRC and to 332 sources in the Culgoora catalog.
For both catalogs, the ratio of PAPER to catalog flux averages to 1, with a
standard deviation of 50%. This measured variation is consistent with
comparisons between independent catalogs observed at different bands. The PAPER
data represent new 145-MHz flux measurements for a large number of sources in
the band expected to encompass cosmic reionization, and represents a
significant step toward establishing a model for removing foregrounds to the
reionization signal.Comment: 3 figures, 2 tables, machine readable table. Accepted by ApJ
Offline and online reconstruction for radio interferometric imaging
Radio astronomy is transitioning to a big-data era due to the emerging
generation of radio interferometric (RI) telescopes, such as the Square
Kilometre Array (SKA), which will acquire massive volumes of data. In this
article we review methods proposed recently to resolve the ill-posed inverse
problem of imaging the raw visibilities acquired by RI telescopes in the
big-data scenario. We focus on the recently proposed online reconstruction
method [4] and the considerable savings in data storage requirements and
computational cost that it yields.Comment: 4 pages; 2 figures; URSI GASS 2020. arXiv admin note: substantial
text overlap with arXiv:1712.0446
On a method to resolve the nuclear activity in galaxies as applied to the Seyfert 2 galaxy NGC1358
Nuclear regions of galaxies generally host a mixture of components with
different exitation, composition, and kinematics. Derivation of emission line
ratios and kinematics could then be misleading, if due correction is not made
for the limited spatial and spectral resolutions of the observations.The aim of
this paper is to demonstrate, with application to a long slit spectrum of the
Seyfert 2 galaxy NGC 1358, how line intensities and velocities, together with
modelling and knowledge of the point spread function, may be used to resolve
the differing structures. In the situation outlined above, the observed
kinematics differs for different spectral lines. From the observed intensity
and velocity distributions of a number of spectral lines and with some
reasonable assumptions to diminish the number of free parameters, the true line
ratios and velocity structures may be deduced. A preliminary solution for the
nuclear structure of NGC 1358 is obtained, involving a nuclear point source and
an emerging outflow of high exitation, as well as a nuclear emission line disk
rotating in the potential of a stellar bulge and expressing a radial excitation
gradient. The method results in a likely scenario for the nuclear structure of
the Seyfert 2 galaxy NGC 1358. For definitive results an extrapolation of the
method to two dimensions combined with the use of integral field spectroscopy
will generally be necessary.Comment: Accepted for Publication in The Astrophysical Journa
The application of compressive sampling to radio astronomy I: Deconvolution
Compressive sampling is a new paradigm for sampling, based on sparseness of
signals or signal representations. It is much less restrictive than
Nyquist-Shannon sampling theory and thus explains and systematises the
widespread experience that methods such as the H\"ogbom CLEAN can violate the
Nyquist-Shannon sampling requirements. In this paper, a CS-based deconvolution
method for extended sources is introduced. This method can reconstruct both
point sources and extended sources (using the isotropic undecimated wavelet
transform as a basis function for the reconstruction step). We compare this
CS-based deconvolution method with two CLEAN-based deconvolution methods: the
H\"ogbom CLEAN and the multiscale CLEAN. This new method shows the best
performance in deconvolving extended sources for both uniform and natural
weighting of the sampled visibilities. Both visual and numerical results of the
comparison are provided.Comment: Published by A&A, Matlab code can be found:
http://code.google.com/p/csra/download
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