Omega Cass: a new multimode NIR-imager/spectrometer for the Calar Alto Observatory

Omega Cass is the new MPIA multi-mode camera for imaging and spectroscopy at near IR wavelengths between 1.0 and 2.5 micrometers . The Camera is equipped with an 1024 X 1024 HAWAII HgCdTe focal plane array from Rockwell. The cryogenic re- imaging optics are designed to cover a wide variety of observing conditions. The imaging scales can be changed during observations, allowing the observer to react to changing conditions. Three different lens sets provide scales of 0.3, 0.2 and 0.1 arcsec/pixel at the f/10 Cassegrain focus of the 3.5m telescope. In combination with a laser based adaptive optics system, available at the same telescope, these imaging scale correspond to 0.12, 0.08 and 0.04 arcsec/pixel, which double samples the diffraction limit at the shortest operation wavelength. A set of grisms allow low to medium resolution long slit spectroscopy up to R equals 1000. In addition, sensitive polarimetry can be done with Wollaston prisms and wire grid analyzers. Omega-Cass is mainly designed for the 3.5m telescope on Calar Alto, although it may be used at any other telescopes with a focal ratio slower than f/8, including the MPIA's 2.2m telescopes on Calar Alto and La Silla.