75 research outputs found
MORESANE: MOdel REconstruction by Synthesis-ANalysis Estimators. A sparse deconvolution algorithm for radio interferometric imaging
(arXiv abridged abstract) The current years are seeing huge developments of
radio telescopes and a tremendous increase of their capabilities. Such systems
make mandatory the design of more sophisticated techniques not only for
transporting, storing and processing this new generation of radio
interferometric data, but also for restoring the astrophysical information
contained in such data. In this paper we present a new radio deconvolution
algorithm named MORESANE and its application to fully realistic simulated data
of MeerKAT, one of the SKA precursors. This method has been designed for the
difficult case of restoring diffuse astronomical sources which are faint in
brightness, complex in morphology and possibly buried in the dirty beam's side
lobes of bright radio sources in the field. MORESANE is a greedy algorithm
which combines complementary types of sparse recovery methods in order to
reconstruct the most appropriate sky model from observed radio visibilities. A
synthesis approach is used for the reconstruction of images, in which the
synthesis atoms representing the unknown sources are learned using analysis
priors. We apply this new deconvolution method to fully realistic simulations
of radio observations of a galaxy cluster and of an HII region in M31. We show
that MORESANE is able to efficiently reconstruct images composed from a wide
variety of sources from radio interferometric data. Comparisons with other
available algorithms, which include multi-scale CLEAN and the recently proposed
methods by Li et al. (2011) and Carrillo et al. (2012), indicate that MORESANE
provides competitive results in terms of both total flux/surface brightness
conservation and fidelity of the reconstructed model. MORESANE seems
particularly well suited for the recovery of diffuse and extended sources, as
well as bright and compact radio sources known to be hosted in galaxy clusters.Comment: 17 pages, 11 figures, accepted for publication on A&
SHAPEMOL: a 3-D code for calculating CO line emission in planetary and protoplanetary nebulae. Detailed model fitting of the complex nebula NGC 6302
Modern instrumentation in radioastronomy constitutes a valuable tool for
studying the Universe: ALMA has reached unprecedented sensitivities and spatial
resolution, while Herschel/HIFI has opened a new window for probing molecular
warm gas (~50-1000 K). On the other hand, the software SHAPE has emerged in the
past few years as a standard tool for determining the morphology and velocity
field of different kinds of gaseous emission nebulae via spatio-kinematical
modelling. SHAPE implements radiative transfer solving, but it is only
available for atomic species and not for molecules. Being aware of the growing
importance of the development of tools for simplifying the analyses of
molecular data, we introduce shapemol, a complement to SHAPE, with which we
intend to fill the so-far under-developed molecular niche. shapemol enables
user-friendly, spatio-kinematic modelling with accurate non-LTE calculations of
excitation and radiative transfer in CO lines. It allows radiative transfer
solving in the 12CO and 13CO J=1-0 to J=17-16 lines, but its implementation
permits easily extending the code to different molecular species. shapemol
allows easily generating synthetic maps and line profiles to match against
interferometric or single-dish observations. We fully describe shapemol and
discuss its limitations and the sources of uncertainty to be expected in the
final synthetic profiles or maps. As an example of the power and versatility of
shapemol, we build a model of the molecular envelope of the planetary nebula
NGC 6302 and compare it with 12CO and 13CO J=2-1 interferometric maps from SMA
and high-J transitions from Herschel/HIFI. We find the molecular envelope to
have a complex, broken ring-like structure with an inner, hotter region and
several 'fingers' and high-velocity blobs, emerging outwards from the plane of
the ring. We derive a mass of 0.11 Msun for the molecular envelope.Comment: 19 pages, 15 figures. Accepted for publication in Astronomy &
Astrophysic
Development of a Powerwall-based solution for the manual flagging of radio astronomy data from eMerlin
This project was created with the intention of establishing an optimisation method for the manual flagging of interferometric data of the eMerlin radio astronomy array, using a Powerwall as a visualisation tool. The complexity of this process which is due to the amount of variables and parameters demands a deep understanding of the data treatment. Once the data is achieved by the antennas the signals are correlated. This process generates undesired signals which mostly coming from radio frequency interference. Also when the calibration is performed some values can mislead the expected outcome. Although
the flagging is supported with algorithms this method is not one hundred percent accurate. That is why visual inspection is still required. The possibility to use a Powerwall as a visualisation system allows different and new dynamics in terms of the interaction of the analyst with the information required to make the flagging
Portuguese SKA white book
Sem resumo disponível.publishe
Radio frequency over fiber technology for SKA-low receiver
The signal reception chain is an essential element for achieving the square kilometer array-low (SKA-low) system requirements in terms of high sensitivity and dynamic range. The balance between gain, linearity, and low power consumption, as well as the cost, are fundamental parameters that influence the selection of the most suitable technology for SKA-low. Further factors, such as low self-generated radio frequency (RF) interference, high reliability, robustness under extreme environment, and last but not least, the distance between the antennas and the acquisition systems, have impacts on the selection for both architecture and receiver system design. The selected technology for the SKA-low RF signal transportation is RF-over-fiber systems, where the preamplified RF signal picked up by the antennas is carried via analogue modulation over optical fiber. The rationales behind the selection are reported, along with descriptions on the development of the receiver prototypes. The prototypes were deployed and installed on the demonstrator arrays at the selected SKA-low site in Western Australian. Particular attention has been put on the thermal characterization of the receiver system under the actual operating temperature on site, especially when both transmitting part and the optical medium are subjected to external ambient temperature variations. Performance issues encountered in the demonstrator arrays are also discussed along with some proposals for future activities
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