Objective-Prisms on Schmidt Telescopes: Past Activity and Future Prospects

Abstract

Objective-prisms combined with wide field Schmidt Telescopes have been used for a wide variety of astronomical studies over the last 20 years ranging from searches for quasars, emission line objects and carbon stars to crude galaxy redshift determinations, galactic studies and investigations into automatic stellar spectral typing. For example, a good low-dispersion UK Schmidt Telescope (UKST) objective-prism plate can contain 60000 useful spectra. Despite this wealth of spectral information, objective-prisms remain a minor activity of most large Schmidts. This is partly because prism exposures are sensitive to observing conditions and many projects require good seeing to produce really useful exposures. Prism spectra can also suffer severe problems with selection effects. Furthermore standard objective-prism searches for unusual objects or large-scale spectroscopic/radial velocity surveys are now in competition with other more effective techniques (e.g. multi-colour or multi-wavelength surveys and multi-object spectroscopy with fibres/slits). Nevertheless good quality, wide-field objective-prism exposures remain an effective discovery tool for many purposes.