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Polarimetric Observations (polarimetric + observation)

Distribution by Scientific Domains

Physics and Astronomy	100%

Selected Abstracts

Polarimetric observations of a sample of Compact Steep-Spectrum sources

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
F. Mantovani
Abstract Measurements of the polarised emission from Compact Steep-Spectrum (CSS) sources can give important information about the physical conditions inside and around the region of radio emission, essentially on the Narrow Line Region. We have observed the sample of CSS sources constructed by Fanti et al. (1990) with the Effelsberg 100-m radio telescope at four frequencies between 2.7 GHz and 10.4 GHz in order to measure the polarisation parameters. Results from the NRAO VLA Sky Survey (Condon et al. 1998) at 1.4 GHz were combined with our measurements for the full sample. The sample is considered statistically complete and allows comprehensive statistical analysis. Some of our conclusions are in disagreement with previous results obtained by polarimetric observations of other samples, for example the B3-VLA sample (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Linear polarization in small radio sources

ASTRONOMISCHE NACHRICHTEN, Issue 5-6 2006
A. Rossetti
Abstract Polarimetric observations at 5 and 8.4 GHz have been performed for 3 CSS quasars. These observations are part of a programme aimed at studying the polarization characteristics of the core regions, jets, and lobes in such objects and at possibly finding of jet-cloud interactions in CSSs. The behaviour of the fractional polarization and of the observed polarization angle as a function of ,2 provides information on the density distribution of the ISM embedding the radio source, on its clumpiness and on the ordered and random components of the interstellar magnetic field. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Asteroid photometric and polarimetric phase curves: Joint linear-exponential modeling

METEORITICS & PLANETARY SCIENCE, Issue 12 2009
K. Muinonen
Here we model the two phase curves jointly at phase angles ,25° using a linear-exponential model, accounting for the opposition effect in disk-integrated brightness and the negative branch in the degree of linear polarization. We apply the MCMC methods to V-band phase curves of asteroids 419 Aurelia (taxonomic class F), 24 Themis (C), 1 Ceres (G), 20 Massalia (S), 55 Pandora (M), and 64 Angelina (E). We show that the photometric and polarimetric phase curves can be described using a common nonlinear parameter for the angular widths of the opposition effect and negative-polarization branch, thus supporting the hypothesis of common physical mechanisms being responsible for the phenomena. Furthermore, incorporating polarimetric observations removes the indeterminacy of the opposition effect for 1 Ceres. We unveil a trend in the interrelation between the enhancement factor of the opposition effect and the angular width: the enhancement factor decreases with decreasing angular width. The minimum polarization and the polarimetric slope at the inversion angle show systematic trends when plotted against the angular width and the normalized photometric slope parameter. Our new approach allows improved analyses of possible similarities and differences among asteroidal surfaces. [source]

Interstellar extinction and polarization , a spheroidal dust grain approach perspective

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2010
H. K. Das
ABSTRACT We extend and investigate the spheroidal model of interstellar dust grains used to simultaneously interpret the observed interstellar extinction and polarization curves. We compare our model with similar models recently suggested by other authors, study its properties and apply it to fit the normalized extinction A(,)/AV and the polarizing efficiency P(,)/A(,) measured in the near-infrared to far-ultraviolet region for several stars seen through one large cloud. We conclude that the model parameter , being the angle between the line of sight and the magnetic field direction can be more or less reliably determined from comparison of the theory and observations. This opens a way to study the spatial structure of interstellar magnetic fields by using multiwavelength photometric and polarimetric observations. [source]

1.4-GHz polarimetric observations of the two fields imaged by the DASI experiment

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
G. Bernardi
ABSTRACT We present results of polarization observations at 1.4 GHz of the two fields imaged by the DASI experiment (,= 23h30m, ,=,55° and ,= 00h30m, ,=,55°, respectively). Data were taken with the Australia Telescope Compact Array with 3.4-arcmin resolution and ,0.18-mJy beam,1 sensitivity. The emission is dominated by point sources, and we do not find evidence for diffuse synchrotron radiation even after source subtraction. This allows to estimate an upper limit of the diffuse polarized emission. The extrapolation to 30 GHz suggests that the synchrotron radiation is lower than the polarized signal measured by the DASI experiment by at least two orders of magnitude. This further supports the conclusions drawn by the DASI team itself about the negligible Galactic foreground contamination in their data set, improving by a factor of ,5 the upper limit estimated by Leitch et al. The dominant point-source emission allows us to estimate the contamination of the cosmic microwave background (CMB) by extragalactic foregrounds. We computed the power spectrum of their contribution, and its extrapolation to 30 GHz provides a framework where the CMB signal should dominate. However, our results do not match the conclusions of the DASI team about the negligibility of point-source contamination, suggesting taking into account a source subtraction from the DASI data. [source]