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Long-term measurements of the radio flux density of Cassiopeia A relative to Cygnus A have been carried out at 927, 290, 151.5, and 38 MHz. The mean secular decreases in the radio flux of Cas A are d927 = -(0.73±0.05)% year-1 (for the period 1977.8-1996.8), d290 = -(0.66 ± 0.07)% year-1 (1978.8-1996.85), and d151.5 = -(1.11 ± 0.22)% year-1 (1980.9-1994.8). Using also the results of other studies, d38 = -(.66 ± 0.17)% year-1 (1956-1995.6) and d151.5 = -(.86 ± 0.09)% year-1 (1966.5-1994.8). The temporal nonuniformity of the Cas A flux density decrease is most likely due to random changes in the integrated radio emission of the approximately 300 compact features observed in this source.

Basing on long-term (1977–1994) measurements at frequencies 151.5, 290 and 927 MHz the mean rates of the secular decrease of Cassiopeia A flux density were estimeted as d 151.5 = −(1.11 ± 0.22)% year−1, d 290 = −(0.79 ± 0.09)% year−1 and d 927 = −(0.72 ± 0.06)% year−1, respectively. The decrease of Cassiopeia A flux density is not uniform in time. Moreover, an increase of the flux density was observed (1979–1980). It is argued the cause of the time variations of d v is stochastic variability of the total radio emission of numerous compact radio features located in the diffuse envelope of Cassiopeia A.

SPOrt is an experiment aimed at making a polarization survey of the sky in the microwave range (22-90 GHz) on large angular scales (FWHM = 7degrees).

The BaR-SPOrt experiment is designed to measure the E -mode power spectrum of the Cosmic Microwave Background Polarization (CMBP) in the multipole range 50 l < 1000. In the current configuration at 32 GHz it can explore up to l = 400. Recent low frequency observations of the target region show that the synchrotron emission should not contamine the CMBP already at 32 GHz. A 6-month observation of a 6° × 6° sky area during the polar night, in ideal environmental conditions, will allow the Italian-French collaboration to both measure the E –mode power spectrum with appropriate sensitivity and perform important tests of the anomalous dust emission. The BaR-SPOrt 32 GHz instrument, now under test and ready for operations by Spring 2005, is proposed for 1–2 years Winter operations at Dome C.

SPOrt is an ASI-funded experiment specifically designed to measure the sky polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be flown on the International Space Station. Starting in 2006 and for at least 18 months, it will be taking direct and simultaneous measurements of the Stokes parameters Q and U at 660 sky pixels, with FWHM=7 degrees. Due to development efforts over the past few years, the design specifications have been significantly improved with respect to the first proposal. Here we present an up-to-date description of the instrument, which now warrants a pixel sensitivity of 1.7 microK for the polarization of the cosmic background radiation, assuming two years of observations. We discuss SPOrt scientific goals in the light of WMAP results, in particular in connection with the emerging double-reionization cosmological scenario., 53 pages, 22 figures, 1 reference replaced

BaR-SPOrt (Balloon-borne Radiometers for Sky Polarisation Observations) is an experiment to measure the linearly polarized emission of sky patches at 32 and 90 GHz with sub-degree angular resolution. It is equipped with high sensitivity correlation polarimeters for simultaneous detection of both the U and Q stokes parameters of the incident radiation. On-axis telescope is used to observe angular scales where the expected polarization of the Cosmic Microwave Background (CMBP) peaks. This project shares most of the know-how and sophisticated technology developed for the SPOrt experiment onboard the International Space Station. The payload is designed to flight onboard long duration stratospheric balloons both in the Northern and Southern hemispheres where low foreground emission sky patches are accessible. Due to the weakness of the expected CMBP signal (in the range of microK), much care has been spent to optimize the instrument design with respect to the systematics generation, observing time efficiency and long term stability. In this contribution we present the instrument design, and first tests on some components of the 32 GHz radiometer., Comment: 12 pages, 10 figures, Astronomical Telescopes and Instrumentation (Polaimetry in Astronomy) Hawaii August 2002 SPIE Meeting

BaR-SPOrt, funded by ASI (Italian Space Agency), is a 32 (90) GHz balloon-borne correlation polarimeter for direct measurements of the Q and U Stokes parameters, with an angular resolution of 0.6° (0.2°). Aim of the experiment is the detection of the polarized emission of the diffuse Galactic Background and the Cosmic Microwave Background (CMB). The most likely launch site is Antarctica (2 to 4-week flight). Kiruna (Sweden, 1-week flight) and Svalbard (Norway, > 1-week flight) are possible launch site to observe the Northern sky

SPOrt (Sky Polarization Observatory) is a space experiment to be flown on the International Space Station during Early Utilization Phase aimed at measuring the microwave polarized emission with FWHM = 7deg, in the frequency range 22-90 GHz. The Galactic polarized emission can be observed at the lower frequencies and the polarization of Cosmic Microwave Background (CMB) at 90 GHz, where contaminants are expected to be less important. The extremely low level of the CMB Polarization signal (< 1 uK) calls for intrinsically stable radiometers. The SPOrt instrument is expressly devoted to CMB polarization measurements and the whole design has been optimized for minimizing instrumental polarization effects. In this contribution we present the receiver architecture based on correlation techniques, the analysis showing its intrinsic stability and the custom hardware development carried out to detect such a low signal., 9 pages, 5 figures, conference proceeding, to appear in "Polarimetry in Astronomy", SPIE Symposium on 'Astronomical Telescopes and Instrumentation', Waikoloa, August 22-28 2002

Multifrequency polarization observations of a number of regions of the Galaxy in the frequency range 200-1250 MHz have been carried out. The area of enhanced linear polarization at meter wavelengths around α1950=4h30m, δ1950=61° (l=146°47′,b=9°03′) reveals a nonmonotonic, oscillating spectrum of the polarized brightness temperature. On the contrary, the region of the North Celestial Pole (l=123°,b=27°24′) has practically monotonic spectrum. The possible reasons for this difference are discussed.

Polarization observations of the Galactic radio emission at 8.3 GHz were made by the 32-m Medicina (Italy) radio telescope in four pixels (HPBW=4.′8). A method of tracking around the upper culmination was used in order to use the rotation of the parallactic angle for detecting the weak linearly polarized Galactic radio emission against the background of relatively strong and variable spurious and instrumental polarization. The well known source 3C 286 was used as calibrator. As a result the brightness temperatures of linearly polarized component of the Galactic radio emission and positions angles were measured for all pixels. Comparison was made for the pixels in the first Galactic quadrant with Duncan et al. 2695 MHz polarization measurements and as a result spectral indexes and rotation measures were determined.

The Moon could be the best external calibrator for the Sky Polarization Observatory (SPOrt) experiment, providing the highest polarized signal at large angular scales (⩾7 °) in the 22–90 GHz range. Maps of linearly polarized lunar radio emission have been realized at 8.3 GHz with the 32-m radiotelescope of IRA-CNR (Medicina-Italy) at full Moon, new Moon, first and last quarter. We derived estimates of spectral and time properties of both the intensity and the linear polarization of the Moon radio emission, taking into account the radiative transfer of heat in lunar soil and the surface roughness. A comparison between predictions of the theory and observations is presented.

SPOrt is a space experimental aimed at studying the polarization of the CMB and of the diffused Galactic Background in the microwave range (22-90 GHz). Here we present the project as well as its main scientific goals.