The second-generation CCD/Transit Instrument (CTI-II) precision astrometric and photometric survey

Abstract

We are implementing the second-generation CCD/Transit Instrument (CTI-II), a unique 1.8-m imaging astrometric and photometric telescope. We discuss design aspects of CTI-II, including the optical system, structure, focal plane mosaic and the detector readout system that allows precise astrometric and photometric measurements. The scientific design drivers for the imaging telescope include discovery and measurement of motion and distance for late M, L and T stars, synoptic photometric monitoring of active galactic nuclei (AGN), and discovery and near real-time spectroscopic followup of distant supernovae and AGN outbursts. These projects drive the design of the wide field-of-view stationary telescope that employs the time-delay and integrate (TDI) readout mode for CCD detectors to produce a deep, multicolor image of the sky every clear night. Nightly observation of the same strip of the sky produces the time domain photometric and repeated astrometric measurements required by the science drivers. The telescope, its focal plane mosaic and the data system all incorporate unique and innovative elements that support an unbiased survey of the sky with intensive time-domain sampling. We review these aspects of the project, and describe steps taken to support the astrometric and photometric precision required by the scientific mission of the telescope.