Search

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.

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 review the measurements of the cosmic background anisotropies at all angular scales. Special attention is devoted to experimental problems and questions concerning the data analysis.

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.

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

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.

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.