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We describe a system of capacitive transducers applied to two free falling objects with the aim of detecting differential accelerations due to nonNewtonian components. The two objects have a cylindrical shape to minimize the systematic errors and they fall in a microgravity condition inside a vacuum tube released by a stratospheric balloon at an altitude of 40 km. The calibration of the capacitive transducers performed in laboratory has shown that it is possible to detect differential accelerations Δa ≲ 1.4 × 10−10 m s−2.

COBE has provided preliminary results on the spectral distribution of both Cosmic Background Radiation (CBR) brightness and dipole anisotropy. We combine these data in order to compare COBRA results with those of COBE and to obtain more stringent upper limits to CBR spectral distortions. The possibility of having detected extragalactic diffuse lines is discussed.

The last few years have seen a large development of mm technology and ultra-sensitive detectors devoted to microwave astronomy and astrophysics. The possibility to deal with large numbers of these detectors assembled into multi--pixel imaging systems has greatly improved the performance of microwave observations, even from ground--based stations, especially combining the power of multi--band detectors with their new imaging capabilities. Hereafter, we will present the development of a multi--pixel solution devoted to Sunyaev--Zel'dovich observations from ground--based telescopes, that is going to be operated from the Millimetre and Infrared Testagrigia Observatory., 5 pages, 3 figures, to be published in th eProceedings of the 2K1BC Workshop, July 9-13, 2001 - Breuil-Cervinia

We have deduced the cosmic microwave background (CMB) temperature in the Coma cluster (A1656, $z=0.0231$), and in A2163 ($z=0.203$) from spectral measurements of the Sunyaev-Zel'dovich (SZ) effect over four passbands at radio and microwave frequencies. The resulting temperatures at these redshifts are $T_{Coma} = 2.789^{+0.080}_{-0.065}$ K and $T_{A2163} = 3.377^{+0.101}_{-0.102}$ K, respectively. These values confirm the expected relation $T(z)=T_{0}(1+z)$, where $T_{0}= 2.725 \pm 0.002$ K is the value measured by the COBE/FIRAS experiment. Alternative scaling relations that are conjectured in non-standard cosmologies can be constrained by the data; for example, if $T(z) = T_{0}(1+z)^{1-a}$ or $T(z)=T_{0}[1+(1+d)z]$, then $a=-0.16^{+0.34}_{-0.32}$ and $d = 0.17 \pm 0.36$ (at 95% confidence). We briefly discuss future prospects for more precise SZ measurements of $T(z)$ at higher redshifts., 13 pages, 1 figure, ApJL accepted for publication

We describe a measurement of the angular power spectrum of anisotropies in the Cosmic Microwave Background (CMB) from 0.3 degrees to ~10 degrees from the North American test flight of the BOOMERANG experiment. BOOMERANG is a balloon-borne telescope with a bolometric receiver designed to map CMB anisotropies on a Long Duration Balloon flight. During a 6-hour test flight of a prototype system in 1997, we mapped > 200 square degrees at high galactic latitudes in two bands centered at 90 and 150 GHz with a resolution of 26 and 16.6 arcmin FWHM respectively. Analysis of the maps gives a power spectrum with a peak at angular scales of ~1 degree with an amplitude ~70 uK., 5 pages, 1 figure LaTeX, emulateapj.sty

The linear polarization degree of the cosmological background has been investigated at angular scales ranging between 0.5/sup 0/ and 40/sup 0/ by means of a balloon-borne far-infrared polarimeter. An upper limit has been found of 8 x 10/sup -/4 at 40/sup 0/ (at one standard deviation). Some cosmological implications are discussed.

We show how combined large-beam infra-red and radio observations toward the Virgo Cluster may be explained by assuming the existence of a large tepid halo surrounding the giant galaxy M87. Such a halo would be able to close the cluster gravitationally. If interpreted as being due to bremmstrahlung radiation by a tepid extended halo, it also explains the infra-red observations, and it has important implications for the physics of M87.

For Assess II, the Spacelab mission simulation conducted in mid-1977, four payload specialists aboard a Convair 990 research aircraft performed six American and six European experiments during nine research flights each of six hours duration in order to evaluate the compatibility of training and experimental design. Mission organization and some initial data from the European experiments are reported. The experiments, conducted over the western U.S., involved infrared astronomy, solar brightness temperature, lidar, airglow TV, and a medical experiment for which physiological parameters were monitored. Conclusions concerning general principles of experiment design are discussed.

We investigate the rotation of the polarization planes for radiation freely traveling in homogeneous anisotropic spaces (Brans effect). Solving the parallel-transport equations in Bianchi type-I and type-V spaces, we find that the rotation angle is at most about 1 rad. The scrambling of the polarization states due to the Brans effect and the finite thickness of the last-scattering surface is negligible in any realistic model, so that any primeval polarization can survive up to the present epoch.

We analyse the spectral shape and possible spurious distortions of the Sunyaev-Zel'dovich effect, arising from the interaction of the cosmic background radiation with hot gases of rich clusters, in the millimetric region. We show that one can measure this effect with high accuracy with present-day infrared detectors, obtaining a larger amount of information than by using radio systems. In particular, one can accurately measure the temperature of the cosmic background radiation without the usual absolute calibration of the detector.

Noise measurements in the frequency regions 5-200 HZ and 5.2 x 10/sup -4/ -8.3 x 10/sup -3/ Hz have been performed in the wavelength region between 300 and 3000 mu m from the high altitude observatory of Tests Grigia, Italy (3.500 m). In the high frequency region a specially designed Ge bolometer operating in background-limited-infrared-photoconductor conditions matched to a 1.5-m telescope has been used, while at low frequency a radiometer designed for atmospheric transmittance measurements was employed. In both regions no excess noise with respect to the photon noise relative to 300-K blackbody has been detected.

We analyze the anisotropies in the extragalactic infrared background and in the source counts in standard cosmology perturbed by large-scale, small-amplitude density fluctuations. The dipole anisotropy of the diffuse background is connected to the dipole of the cosmic background radiation and of the source counts, and a full consistency with a large (≃ 7%) anisotropy in the IRAS source counts is found to imply a low density (Ω0 ≃ 0.2) universe, contrary to a previous claim. We analyze also higher order harmonics. Using the IRAS Low-Resolution All-Sky Maps we obtain an upper limit of 0.17MJy/sr on the dipole of the 100 μm background and show that it is consistent with a source-count anisotropy of 7% only for a low intensity, I ≤ 1.2 M Jy/sr, of the background itself.

The observations of the Zel'dovich effect in galaxy clusters are reviewed. The failure to detect the effect at short wavelengths is interpreted as proof of the existence of intergalactic dust. Small and fast spinning grains can emit the power needed to compensate the decrease in temperature expected from the Zel'dovich effect.

Quantum fluctuations of the cosmic background have been measured in the 900 to 2000 micron range (H.P.B.W.) by means of a balloon-borne correlator operating between 5 and 150 Hz. Preliminary results indicate an upper limit √2> ≤ 2.1 × 10−17 watt/(cm2 srad Hz)1/2, corresponding to the noise of a blackbody at a temperature T ≤ 3.1 K at 1σ.

The classical cosmological theories, based on the solution of field equations, have encountered a certain number of difficulties. To overcome these, cosmologists tend to consider new theories, especially for the early epochs of the Universe where general relativity is expected to fail.

The possibility of detecting diffuse sky radiation in the (250÷3000) μm range is discussed on the basis of recent measurements performed at the mountain observatory of Testa Grigia (3500 m a.s.l.) on the atmospheric emission and on the atmospheric noise. It is shown how, in many cases, the limits assigned by the residual atmospheric emission are well below the sensitivity of the available infra-red detectors; as a consequence some new experiments of background astronomy are suggested.

Observations carried out from an Alpine location (3500 m) using a Dicke- type radiometer with a broad-band germanium bolometer have proved that the cosmic background radiation in the 900-1400 micron band can be measured from mountain altitudes with a precision comparable with that obtained in the 3.3-mm band. The inaccuracy in the measurements is attributed to calibration rather than to the atmospheric disturbances. The upper limit of 2.7 degreeK observed is more stringent than that of previously reported balloon-borne and rocket-borne observations in the same band. (AIP)

The cosmic-background anisotropy has been investigated at the angular scale of 25 minutes of arc by means of a special isotropometer at the alpine station of Testa Grigia (3500 m above sea level) through the atmospheric window 1.0-1.4 mm. We found an upper limit $\frac{\ensuremath{\Delta}T}{T}\ensuremath{\lesssim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ at two standard deviations. Some physical implications about the origin and the rotation of superclusters and about the secondary ionization of plasma are discussed.

We measured the anisotropy of the cosmic background radiation at the angular scale of 2/sup 0/ in the millimetric wavelength region, in the course of the NASA-ESA ASSESS II Mission. We set upper limits on the anisotropy in several sky regions, the most stringent one being ..delta..T/T

Results of our wide beam radio observations of M87 are given here. Combined with the infrared observations of Virgo (Ceccarelli et al. 1982), we show that in order to explain both the radio and infrared observations, it is convenient to postulate an extended tepid (∼(+5) K ) halo, in addition to a hot (∼(+8) K ) halo surrounding M87. This tepid halo would be able to close the system gravitationally.

Atmospheric transmittance in the band of 300–2000 μm was measured in the far i.r. Solar Observatory of Testa Grigia, 3480m above standard. These measurements are compared with the meteorological data observed at Plateau Rosa in the last 7yr.

In this paper we are dealing with the “throughput” ΩS and with the optical bandwidth Δλ of an IR-detector when it is employed at the focus of a telescope to observe point-like sources. We have found that the maximum signal-to-noise ratio is obtained for ΩS≃ λ2 and Δλ ≃ λ. Under these optimized conditions the quantum noise of the atmosphere is lower than 10−14 W. Hz− 1 2 in the 300–2000 micron range. Because of this the best available far infrared detectors may be used in the atmospheric window at ground based observatories without background limitations.

The photocurrent pinch-off, observed in high resistivity thin CdS crystals subject to a high electric field (field effect), is strongly dependent on the atmosphere surrounding the crystal. The minimum pinch-off voltage has been measured in different atmospheres. This gives a method for the evaluation of several physical quantities relevant to the surface and bulk properties of CdS.

Infrared carbon bolometer detectors operating at liquid helium temperature (LHT) have been constructed. The properties of carbon bolometers which depend upon the thickness of the elements have been investigated, particularly with respect to their responsivity. Responsivities up to 106 V/W may be obtained by decreasing the thickness of the element, without any appreciable loss in the far infrared absorption. By using evaporated gold contacts, a NEP lower than 10−12 W/Hz 1 2 has been obtained in two cases. In practice carbon bolometers appear to be competitive with other liquid helium cooled bolometers.

The investigation of hole mobilityμp in CdS has shown a number of apparently contradictory experimental results. In the present work we examine in some detail the kinetics of the photocurrent under field effect. One finds that the photocurrent pinch-off and the complete recovery give respectivelyμp=0 andμp ≠ 0. The contradiction can be overcome assuming a «surface hole mobility»μps=0 and 24 bulk hole mobility»μpb≠0. Based on this assumption, a simple mathematical model has been developed which appears to describe correctly the photocurrent kinetics under field effect. Furthermore, the results of various authors are well interpreted separating the observations into two groups according to whether the measurement ofμp is done moving the holes at the surface of CdS (μps=0) or through the bulk only (μpb≠0).

We report preliminary results relative to a balloon-borne search for the large-scale anisotropy carried out in 1980 by means of two far infrared photometers centered at 400 and 1100 microns. While these results are consistent with those obtained in an earlier flight, the second, shorter wavelength channel included in the 1980 work provides interesting insights into the influence of galactic dust on such far infrared observations.

We have evaluated the accuracy in maintaining the differential modulation parallel to the horizon, which is required to reduce the atmospheric background below the detector noise in an infrared telescope operating under optimized conditions.

A photopolarimeter has been designed to measure the possible polarization of the Cosmic Background Radiation at millimeter wavelengths. The instrument and the working principle are described together with the testing procedure.

Results concerning zodiacal dust emission are reported from an IR sky survey experiment performed during a balloon flight on July 30, 1984 which explored five wavelength bands centered at 11, 19, 50, 108, and 225 microns. The dust density n decreases at a rate slower than r exp -1.3 with increasing heliocentric distance. The trend of n depends critically on the radial variation of the temperature which, in turn, depends on the chemical composition of the grains. The spatial distribution of the dust is in good agreement with that previously inferred from IR measurements. A comparison between IR and optical observations points out the uncertainties affecting the estimates of the dust density obtained with both methods. The emission spectrum of the dust is used to discriminate among the different species of grains, showing that the observations can be accounted for by an appropriate mixture of graphite and silicates. 18 references.

We have measured the sky temperature trough the 7-10cm−1 atmospheric window from the Alpine station of Testa Grigia(3500m. a.s.l.). An upper limit of 2.7°K has been found.

The BOOMERanG experiment is a stratospheric balloon telescope intended to measure the Cosmic Microwave Background anisotropy at angular scales between a few degrees and ten arcminutes. The experiment features a wide focal plane with 16 detectors in the frequency bands centered at 90, 150, 220, 400 GHz, with FWHM ranging between 18 and 10 arcmin. It will be flown on a long duration (7-14 days) flight circumnavigating Antarctica at the end of 1998. The instrument was flown with a reduced focal plane (6 detectors, 90 and 150 GHz bands, 25 to 15 arcmin FWHM) on a qualification flight from Texas, in August 1997. A wide (~300 sq. deg, i.e. about 5000 independent beams at 150 GHz) sky area was mapped in the constellations of Capricornus, Aquarius, Cetus, with very low foreground contamination. The instrument was calibrated using the CMB dipole and observations of Jupiter. The LDB version of the instrument has been qualified and shipped to Antarctica., 12 pages, 9 figures

Weber's theoretical calculations concerning photoconductivity of semiconductors in a transverse electric field are extended to two particular models for CdS single crystals. An agreement with experiment is found when photoexcitation is weak; the presence of surface states is pointed out.