Rapid Photoelectric Spectrum Scanning Techniques

Extract

Photoelectric spectrophotometry has been pursued with increasing success in recent years. In studies of single line profiles, restricted spectral regions, or stellar continua at low resolution, the photomultiplier offers an increase in speed of up to 20 times over the photographic emulsion and an output directly proportional to light intensity over a wide range of intensity. Difficulties in slow scanners have been caused chiefly by fluctuations in light due to seeing, guiding and extinction changes, necessitating either wide slits and photometric weather or ratio circuits. The technique of rapid scanning and exact superposition of digital data from rapid scans offers a solution to these problems. The basic requirement for rapid scanning is therefore a multichannel analyser and a suitable triggering mechanism. I shall describe briefly the way this is being developed at the 48-inch telescope coudé of the Dominion Astrophysical Observatory, and other uses this instrument is being put to.