S-Cam: An imaging spectro-photometer based on superconducting tunnel junctions

S-Cam is a cryogenic camera for ground-based astronomy using Superconductin g Tunnel Junctions (STJs). It has been designed as a technology demonstrato r, aiming to prove the potential of a new generation of single photon count ing detectors at a ground-based telescope. The camera has a field of view o f about 4.0 x 4.0 arcsec(2) and it is based on a 6 x 6 array of Ta-Al Josep hson junctions, operating at about 350 mK and individually read-out. For ea ch detected photon, the absorption position, the arrival time and the corre sponding energy are measured. In this paper we provide an overview of the c ryogenic detector performance, a description of the S-Cam system and a summ ary of the results obtained both during testing at ESTEC and during the fir st observations at the William Herschel Telescope in La Palma (Canary Islan ds, Spain). Initial astronomical results on the Crab pulsar are presented a long with an outlook on future activities.