Charge-coupled device (CCD)/transit instrument (CTI) deep photometric and polarimetric survey—a progress report

We have previously reported on the conceptual design and predicted performance of a new type of dedicated astronomical telescope to be used for a deep photometric survey for galactic and extragalactic variability and polarization. Data derived from this survey will be useful for a wide variety of astronomical investigations including the definition of a complete sample of QSOs, based on their variability and nonstellar colors, the detection of supernovae on the rising branch of their light curves, and the determination of the super-nova production rate as a function of galaxy color, morphology and redshift. The telescope we are producing to accomplish this survey is a transit instrument. It will incorporate a 1.8 m primary mirror of very high quality, fabricated as part of the program to develop the Space Telescope mirror technology, and, as its detectors, two RCA CCDs (512 x 320 x 30 micron pixels) used in the time-delay and integration (TDI) mode. By means of a dichroic beamsplitter the two CCDs view the same region of the sky, subtending about 8.2 arcminutes in declination. The effective integration time on the sky using this technique is about one minute, resulting in a faint limiting magnitude of about 22 per night. The data from the digitized strip of sky is recorded and analyzed in real-time for specific events such as supernovae. The CCD/transit technique has been demonstrated using the Steward Observatory (SO) 2.3 m telescope with the drive switched off. The results of this demonstration are shown and discussed. We report on progress in all aspects of the CTI development including the design of the transit telescope, which is optimized for wide-field, seeing-limited imaging. In particular, we describe a two-mirror field corrector system which realizes the potential image quality of the high precision primary mirror over a wide field and over the wide spectral bandpass of the CCDs.