L. Pizzo

New 3He/4He refrigerator

Abstract The sensitivity increase in bolometers obtained by operating temperatures of 1 K (helium-4) and 0.3 K (helium-3), with respect to standard bolometers cooled at pumped 4He temperature, represents in infrared and submillimetric astronomy a remarkable step forward in applications both on large ground telescopes and on stratospheric balloons. The characteristics are introduced of a double stage refrigerator (4He/3He) which allows a temperature of nearly 300 mK to be reached, starting from a temperature of 4.2 K. No moving parts and external links are involved, except for the electric leads, so as to exploit only the condensation and cryosorption cycles of 4He and 3He, without pumping on the main 4He bath.

The Italian Astrophysical Observatory in Antarctica: OASI

OASI (Infrared and Sub-mm Antarctic Observatory) is the first large telescope permanently installed in Antarctica. It is located close to the Italian Base in Antarctica (Terra Nova Bay Station, latitude: 74.39 S, longitude: 164.09 E). The OASI first light was received in December 1990 when the wobbling secondary mirror was mounted. The telescope is planned to be an open facility which can operate in the wavelengths range between 350 μm and 3mm. The sky coverage from OASI goes down to a declination of about-35° for a 24 hours/day observing time.

Improved 3He/4He refrigerator

Abstract The characteristics and performance of an improved 3 He/ 4 He double stage refrigerator are presented. It is based on the same principle as the previous double stage refrigerator described in reference 1. A new geometry was used to overcome both the extra thermal input due to gas convection in the condensation lines and the long period required to precool at 4.2 K. The improved refrigerator reaches an operative temperature of ≈0.35 K without any external mechanical pumping. The refrigerator has been used to cool 3 He bolometers.

PaperNew 3He/4He refrigerator

Abstract The sensitivity increase in bolometers obtained by operating temperatures of 1 K (helium-4) and 0.3 K (helium-3), with respect to standard bolometers cooled at pumped 4He temperature, represents in infrared and submillimetric astronomy a remarkable step forward in applications both on large ground telescopes and on stratospheric balloons. The characteristics are introduced of a double stage refrigerator (4He/3He) which allows a temperature of nearly 300 mK to be reached, starting from a temperature of 4.2 K. No moving parts and external links are involved, except for the electric leads, so as to exploit only the condensation and cryosorption cycles of 4He and 3He, without pumping on the main 4He bath.

Atmospheric transmission and noise measurements in Antarctica

Abstract We describe a set of measurements carried out in Antarctica during the second Italian Antarctic Expedition. Atmospheric precipitable water vapour, millimetric transmission and noise were monitored for 2 months during the austral summer. The results suggest that the site is favourable for far infrared astronomy measurements.

Millimeter observations of the magellanic clouds

Millimetric observations (1-2 mm) toward the Magellanic Clouds from Antarctica show a good spatial correlation with the IRAS 100-micron emission in the same sky regions. Very likely a cold component coexisting with the warm dust detected by IRAS has been observed. 18 refs.

Millimetric observations of southern HII regions

We report on millimetric continuum observations of two bright compact HII regions, which have been observed for the first time in this frequency range. For the two observed regions (G291.6-0.5 and G291.3-0.7), we derive the flux densities at the two observed wavelengths (1.25 and 2 mm) as well as the spectral index and the temperature of the surrounding dust by fitting a modified blackbody curve to our results combined with IR values obtained from the literature. We also estimate the dust mass and the bolometric luminosity of the two regions.

An improved 3He refrigerator

Abstract The new generation of miniature 3He refrigerators, exploiting only the condensation and cryosorption cycles of 3He without moving parts and external links, represents the most common adopted solution in low temperature physics for cooling detectors such as bolometers at 0.3 K. The characteristics and performance of an improved 3He refrigerator working at a temperature of nearly 0.3 K are discussed. We introduce a new class of refrigerator (patented) which allows one to reach the operating temperature in a much shorter time than with standard 3He refrigerators, without using any thermal switch. The system has the potential to be very useful in all applications where several modifications are required.

Diffuse galactic emission at millimetric wavelengths

Millimetric continuum observations of the Galactic disk at b about -8 deg and l about 290-310 deg has been achieved during the Italian 1987-1988 scientific expedition in Antarctica. Emission was detected from few southern clouds (the Chamaeleon region and a cirrus cloud), and their energy distributions reveal an excess in the long wavelength range. This fact is interpreted as being due to the presence of a cold component of the interstellar material coexisting with the warm dust responsible for the emission detected by IRAS. Then, a multiple nature of the interstellar dust is suggested also in regions far from the Galactic bulge. 45 refs.

Millimetric flux densities as a test of atmospheric turbulence

Abstract In this paper it is shown how submillimetre and millimetre flux density measurements of sky fluctuations can be used to infer the characteristics of atmospheric turbulence. Two different approaches have been followed: first, by considering the observed process as due to the atmospheric turbulence, we used the r.m.s. sky fluctuations to derive some physical parametres characterizing the phenomenon; second, by investigating the power spectrum and the autocorrelation function, we derive an empirical model (the AR model) to try to deduce the physical process. In this case, the fitted power spectrum agrees strikingly with that predicted by the theory of a stationary turbulent flow for the atmosphere in the sampled frequency range. This kind of modeling can help to disentangle the atmospheric fluctuations from the extraterrestrial signal in ground-based astrophysical measurements. Measurements of the water vapour content and atmospheric transmission at the Italian Base in Antarctica, where the data have been taken, at the wavelengths of 350 μm, 1 and 2mm are also reported.