scholarly journals Diffuse polarized emission in the LOFAR Two-meter Sky Survey

2019 ◽  
Vol 623 ◽  
pp. A71 ◽  
Author(s):  
C. L. Van Eck ◽  
M. Haverkorn ◽  
M. I. R. Alves ◽  
R. Beck ◽  
P. Best ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Depth Resolution ◽  
Polarization Data ◽  
Point Spread ◽  
Instrumental Polarization ◽  
Rotation Measure ◽  
Sky Survey ◽  
Spread Function ◽  
Polarized Emission ◽  
The Magnetic Field

Faraday tomography allows us to map diffuse polarized synchrotron emission from our Galaxy and use it to interpret the magnetic field in the interstellar medium (ISM). We have applied Faraday tomography to 60 observations from the LOFAR Two-meter Sky Survey (LOTSS) and produced a Faraday depth cube mosaic covering 568 square degrees at high Galactic latitudes, at 4.′3 angular resolution and 1 rad m−2 Faraday depth resolution, with a typical noise level of 50–100 μJy per point spread function (PSF) per rotation measure spread function (RMSF; 40–80 mK RMSF−1). While parts of the images are strongly affected by instrumental polarization, we observed diffuse polarized emission throughout most of the field, with typical brightness between 1 and 6 K RMSF−1, and Faraday depths between − 7 and +25 rad m−2. We observed many new polarization features, some up to 15° in length. These include two regions with very uniformly structured, linear gradients in the Faraday depth; we measured the steepness of these gradients as 2.6 and 13 rad m−2 deg−1. We also observed a relationship between one of the gradients and an H I filament in the local ISM. Other ISM tracers were also checked for correlations with our polarization data and none were found, but very little signal was seen in most tracers in this region. We conclude that the LOTSS data are very well suited for Faraday tomography, and that a full-scale survey with all the LOTSS data has the potential to reveal many new Galactic polarization features and map out diffuse Faraday depth structure across the entire northern hemisphere.

Comparison of the distributions of galactic y-radiation and radio synchrotron radiation

1981 ◽  
Vol 301 (1462) ◽  
pp. 573-575 ◽  
Keyword(s):  
Radio Emission ◽  
Full Width Half Maximum ◽  
Detailed Comparison ◽  
Full Width ◽  
Half Maximum ◽  
Brightness Temperatures ◽  
Point Spread ◽  
Sky Survey ◽  
Spread Function ◽  
Continuum Radio

We have used the new all-sky survey of continuum radio emission at 408 MHz of Haslam et al. (1981 a, b ) to compare the distribution of radio emission in a band along the galactic equator for [ b ] < 20° with the COS-B y-ray distribution of Mayer-Hasselwander et al. (1980). The radio survey has resolution with full width half-maximum (f.w.h.m.) of 51 arc min and the data are brightness temperatures at 20' intervals in galactic coordinates. Such comparisons have been made before (see, for example, Jakel et al. 1975; Paul et al. 1976; Higdon 1979) with earlier y-ray data but this is the first in which the radio data have been in a form allowing a detailed comparison after convolution with the point spread function of the y-ray detector.

Experimental determination of the effects of boundary reflection on the angular resolution of microphone arrays

2018 ◽  
Vol 25 (3) ◽  
pp. 249-286 ◽  
Author(s):  
Matthew R. Aldeman ◽  
Ganesh Raman
Keyword(s):  
Point Spread Function ◽  
Angular Resolution ◽  
Microphone Array ◽  
Free Field ◽  
Logarithmic Spiral ◽  
Microphone Arrays ◽  
Acoustic Source ◽  
Point Spread ◽  
Wide Range ◽  
Spread Function

The Rayleigh criterion has long been considered the standard criterion for angular resolution of imaging systems, including microphone arrays. However, advanced beamforming methods have been developed in the past 20 years that have dramatically improved the angular resolution of microphone array systems. In this investigation, the angular resolution performance of three scaled microphone arrays and one alternative array geometry were tested with both approximately free-field and reflective boundary conditions. All of the arrays were subjected to a thorough regimen of testing with broadband acoustic sources. Beamforming analysis was performed with the Delay-and-Sum, TIDY, DAMAS, DAMAS2, and CLEAN-SC algorithms. The Delay-and-Sum algorithm is shown to offer the lowest angular resolution performance because it does not separate the acoustic source map from the point spread function of the array. The DAMAS algorithm offers the greatest angular resolution because it numerically deconvolutes the acoustic source map from the point spread function. However, deconvolution-based algorithms (DAMAS and DAMAS2) were the most negatively affected by boundary reflection effects. The logarithmic spiral array is shown to offer versatile performance across a wide range of frequencies, while an alternative quasi-periodic array yields results that are highly frequency-dependent. It is demonstrated that this is because of gaps in the source-to-element differences coverage, and the gaps in coverage correspond to half-wavelengths of frequency bands with significantly lower angular resolution performance.

scholarly journals QSO Color Selection in the SDSS

1998 ◽  
Vol 179 ◽  
pp. 291-292
Author(s):  
H. J. Newberg ◽  
B. Yanny
Keyword(s):  
Critical Path ◽  
Color Space ◽  
Sloan Digital Sky Survey ◽  
Radio Sources ◽  
Color Selection ◽  
The North ◽  
Point Spread ◽  
Sky Survey ◽  
Spread Function ◽  
North Galactic

The Sloan Digital Sky Survey (SDSS) will image 10,000 square degrees in the north galactic cap in five filters. We hope to identify and obtain spectra for about 100,000 quasars brighter than 20th magnitude in this area. The selection will be primarily on the basis of point spread function and colors, but we will also identify quasars from a catalog of FIRST radio sources. The selection areas in color space must be determined during the testing period prior to the official start of the survey. This task may determine the length of the test period. In anticipation of this becoming the critical path, we have written a body of software that will allow us to quickly analyze a set of multicolor data and make a first cut at the selection limits.

scholarly journals A modified algorithm for Cleaning wide-field maps with extended structures

1991 ◽  
Vol 131 ◽  
pp. 242-242
Author(s):  
K. S. Dwarakanath ◽  
A. A. Deshpande ◽  
N. Udaya Shankar
Keyword(s):  
Point Spread Function ◽  
Dynamic Range ◽  
Computing Time ◽  
Point Sources ◽  
Aperture Synthesis ◽  
Wide Field ◽  
Point Spread ◽  
Sky Survey ◽  
Spread Function ◽  
Modified Algorithm

AbstractA simple but effective modification to the conventional CLEAN algorithm is suggested. This modification ensures both stability and speed when CLEAN is applied to maps containing a mixture of point sources and extended structures. The method has been successfully applied to the recently-completed sky survey at 34.5 MHz. This survey was made using the Gauribidanur T array (GEETEE) in 1-D aperture synthesis mode. Since in this case the ‘dirty beam’ (point spread function) cannot be directly computed, a method to obtain this is discussed in detail. The results of this deconvolution procedure have been encouraging in terms of reduced computing time and improved dynamic range in our maps. This algorithm should find wider application in deconvolving maps which have both extended structures and point sources.

Planetary Nebulae Detected in the AKARI Far-IR All-Sky Survey Maps

2018 ◽  
Vol 14 (S343) ◽  
pp. 522-524
Author(s):  
Toshiya Ueta ◽  
Ryszard Szczerba ◽  
Andrew G. Fullard ◽  
Satoshi Takita
Keyword(s):  
Planetary Nebulae ◽  
Correction Method ◽  
Point Spread ◽  
Sky Survey ◽  
Spread Function ◽  
Infrared Astronomical Satellite ◽  
Empirical Point ◽  
The University ◽  
Astronomical Satellite ◽  
Bright Source

AbstractThe AKARI Far-IR All-Sky Survey (AFASS) maps produced by the AKARI Infrared Astronomical Satellite enabled us to probe the far-IR sky for objects having surface brightnesses greater than a few to a couple of dozen MJy sr−1. Recently, we have verified that, if AFASS-measured fluxes are properly corrected for using the aperture correction method based on the empirical point-spread-function templates derived directly from the AFASS maps, point-source photometry measured from the AFASS maps reproduces fluxes in the AKARI bright source catalogue (BSC). We have surveyed the far-IR sky in the AFASS for Galactic planetary nebulae (PNe) based on the University of Hong Kong/Australian Astronomical Observatory/Strasbourg Observatory Hα Planetary Nebula database (HASHPNDB), preliminarily yielding far-IR fluxes for roughly 1000 Galactic PNe including a few hundreds of PNe not listed in the AKARI/BSC.

scholarly journals Point-Spread Function (PSF) Photometric Analysis of Open Clusters: Melotte 72 & NGC 2158

2015 ◽  
Vol 12 (4) ◽  
Author(s):  
Muhammad Mirza ◽  
Zain Rahim
Keyword(s):  
Point Spread Function ◽  
Stellar System ◽  
Open Clusters ◽  
Sloan Digital Sky Survey ◽  
Physical Parameters ◽  
Open Star Clusters ◽  
Open Star ◽  
Point Spread ◽  
Sky Survey ◽  
Spread Function

Point Spread Function (PSF) photometry of open star clusters Melotte 72 and NGC 2158 was performed using g and r band data from the Sloan digital Sky Survey (SDSS) Data Release 7. Instrumental magnitudes of stars in both bands were transformed into calibrated magnitudes using standard equation. Color-Magnitude (CM) diagrams were produced and compared with the SDSS isochrones for AB stellar system for different ages and/or metallicities. The objective of this study was to determine the physical parameters (age, distance, metallicity, reddening) of open clusters from CM diagrams. The best fit isochrones were used to estimate cluster parameters. The observed parameters were then compared with the WEBDA data base. KEYWORDS: PSF Photometry, Melotte 72, SDSS, NGC 2158, Isochrone Fitting, IRAF

scholarly journals A broad-band spectro-polarimetric view of the NVSS rotation measure catalogue – II. Effects of off-axis instrumental polarization

2019 ◽  
Vol 487 (3) ◽  
pp. 3454-3469 ◽  
Author(s):  
Yik Ki Ma ◽  
S A Mao ◽  
Jeroen Stil ◽  
Aritra Basu ◽  
Jennifer West ◽  
...  
Keyword(s):  
Broad Band ◽  
Data Set ◽  
Very Large Array ◽  
Unique Data ◽  
Instrumental Polarization ◽  
Rotation Measure ◽  
Sky Survey ◽  
Systematic Effects ◽  
Cent Level ◽  
Non Gaussian

Abstract The NRAO VLA Sky Survey (NVSS) rotation measure (RM) catalogue has enabled numerous studies in cosmic magnetism, and will continue being a unique data set complementing future polarization surveys. Robust comparisons with these new surveys will however require further understandings in the systematic effects present in the NVSS RM catalogue. In this paper, we make careful comparisons between our new on-axis broad-band observations with the Karl G. Jansky Very Large Array and the NVSS RM results for 23 sources. We found that two unpolarized sources were reported as polarized at about 0.5 per cent level in the RM catalogue, and noted significant differences between our newly derived RM values and the catalogue values for the remaining 21 sources. These discrepancies are attributed to off-axis instrumental polarization in the NVSS RM catalogue. By adopting the 0.5 per cent above as the typical off-axis instrumental polarization amplitude, we quantified its effect on the reported RMs with a simulation, and found that on average the RM uncertainties in the catalogue have to be increased by ${\approx } 10\, {{\ \rm per\ cent}}$ to account for the off-axis instrumental polarization effect. This effect is more substantial for sources with lower fractional polarization, and is a function of the source’s true RM. Moreover, the distribution of the resulting RM uncertainty is highly non-Gaussian. With the extra RM uncertainty incorporated, we found that the RM values from the two observations for most (18 out of 21) of our polarized targets can be reconciled. The remaining three are interpreted as showing hints of time variabilities in RM.

Imaging through Scattering Media with a Learning Based Prior

2020 ◽  
Vol 2020 (14) ◽  
pp. 306-1-306-6
Author(s):  
Florian Schiffers ◽  
Lionel Fiske ◽  
Pablo Ruiz ◽  
Aggelos K. Katsaggelos ◽  
Oliver Cossairt
Keyword(s):  
Optimization Problem ◽  
Autonomous Driving ◽  
Scattering Media ◽  
Photon Scattering ◽  
Point Spread ◽  
Spread Function ◽  
Radiative Transport Equation ◽  
Spatio Temporal ◽  
Transient Imaging

Imaging through scattering media finds applications in diverse fields from biomedicine to autonomous driving. However, interpreting the resulting images is difficult due to blur caused by the scattering of photons within the medium. Transient information, captured with fast temporal sensors, can be used to significantly improve the quality of images acquired in scattering conditions. Photon scattering, within a highly scattering media, is well modeled by the diffusion approximation of the Radiative Transport Equation (RTE). Its solution is easily derived which can be interpreted as a Spatio-Temporal Point Spread Function (STPSF). In this paper, we first discuss the properties of the ST-PSF and subsequently use this knowledge to simulate transient imaging through highly scattering media. We then propose a framework to invert the forward model, which assumes Poisson noise, to recover a noise-free, unblurred image by solving an optimization problem.

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