The two EROS 4k × 8k CCD mosaic cameras

We present our new astronomical imaging system, consisting of two 4k × 8k CCD mosaic cameras, which allows simultaneous imaging in two focal planes with different color passbands. Each mosaic is made of eight 2k × 2k three edge buttable CCDs and is maintained at 180 K by using a fully automated original cryogenic system without LN2. The cameras are mounted on a 1 m Ritchey-Chretien telescope, at the La Silla Observatory in Chile. A modular electronic system permits an individual computer controlled setting and a parallel readout of the CCDs. The resulting 64 Mb per mosaic are transferred with an optical fiber to a VME acquisition crate, which includes the user interface and controls the whole experiment. The enormous data rate is then reduced and treated by a pool of three DEC alpha stations. This system will be used in a sky-survey to search gravitational microlenses, supernovae and red dwarfs.