Calibration and first light of the Diabolo photometer at the Millimetre and Infrared Testa Grigia Observatory

Abstract

Abstract.We have designed and built a largethroughput dual channel photometer, Diabolo. This photometer is dedicated to the observation of millimetre continuum diffuse sources, and in particular, of the SunyaevZel'dovich effect and of anisotropies of the 3K background. We describe the optical layout and filtering system of the instrument, which uses two bolometric detectors for simultaneous observations in two frequency channels at 1.2 and 2.1 mm . The bolometers are cooled to a working temperature of 0.1 K provided by a compact dilution cryostat. The photometric and angular responses of the instrument are measured in the laboratory. First astronomical light was detected in March 1995 at the focus of the new Millimetre and Infrared Testa Grigia Observatory (MITO) Telescope. The established sensitivity of the system is of 7 mK RJ s 1/2 . For a typical map of at least 10 beams, with one hour of integration per beam, one can achieve the rms values of y SZ 7 × 10 −5 and the 3K background anisotropy ∆T T 7 × 10 −5 , in winter conditions. We also report on a novel bolometer AC readout circuit which allows for the first time total power measurements on the sky. This technique alleviates (but does not forbid) the use of chopping with a secondary mirror. This technique and the dilution fridge concept will be used in future scan-modulated space instrument like the ESA Planck mission project.

Planckpre-launch status: The HFI instrument, from specification to actual performance

“…A number of technical developments necessary for HFI were tested in pathfinder ground-based and balloon-borne instruments, like SuZIE , Diabolo (Benoît et al 2000), BOOMERANG (Piacentini et al 2002;Crill et al 2003;Masi et al 2006), and MAXIMA (Lee et al 1999). Essential aspects of the HFI design concept were verified with the balloonborne Archeops instrument (Benoît et al 2002), whose focal plane instrument closely followed the design of HFI.…”

Archeops: a high resolution, large sky coverage balloon experiment for mapping cosmic microwave background anisotropies

“…16), which is easily detected by simple lockin on the bolometer signal with respect to the thermal background. The source has been tested at the Plateau de Bure observatory by measuring the main lobe of the POM2 telescope coupled to the Diabolo cryostat [Benoît et al, 2000]. Some preliminary measurements were performed at close positions at Trapani just before the flight.…”

MAD-4-MITO, a multi array of detectors for ground-based mm/submm SZ observations

“…on the Alps, just along the Italian/Swiss border line. The station, famous for the good atmospheric conditions and low water vapour content (less than 1mm during Winter months, with minimum peaks in December/January), ensures ideal observing conditions for microwave experiments, and has been used by the Rome group along the years as operating base for its main single-pixel SZ-devoted experiment [6], and as a benchmark site for the Diabolo cryostat [7]. The telescope has an aberration-free field of view of 20', which will be fully pixelized from the MAD optic system.…”