Implementation and Use of Wide Fields in Future Very Large Telescopes

Abstract

AbstractThe full potential of the next generation of larger telescopes will be realized only if they have well instrumented large fields of view. Scientific problems for which very large ground-based optical telescopes will be of most value often will need surveys to very deep limits with imaging and slitless spectroscopy, followed by spectroscopy of faint objects taken many at once over the field. Improved instruments and detectors for this purpose are being developed. Remotely positioned fibers allow the coupling of light from many objects in the field to the spectrograph slit. CCD arrays, operated in the TDI or drift scan mode, will make large area detectors of high efficiency that may supercede photographic plates. An ideal telescope optical design should be based on a fast parabolic primary, have a field of at least 1° with achromatic images < 0.25 arcseconds and have provision for dispersive elements to be used for slitless spectroscopy and compensation of atmospheric dispersion over the full field. A good solution for a general purpose telescope that can satisfy these needs is given by a three element refractive corrector at a fast Cassegrain focus. A specialized telescope dedicated to sky surveys, with better image quality and higher throughput than presently available, might be built as a scaled up Schmidt with very large photographic plates. Better performance in most areas should be obtained with a large CCD mosaic detector operated in the drift scan mode at a telescope with a 2-mirror reflecting corrector.