Abstract
ABSTRACT An automatic photometer which provides repetitive, rapid filter cycling and star-to-sky chopping in each filter with mechanical simplicity and convenience is described. All the mechanical motion is accomplished with a single stepper motor, filter wheel and chopper disk being mounted directly on its shaft and turning as one moving part, providing high precision and reliability of color photometry. The electronics for data handling and control of the photometer included a hard wired logic stepper control system and a multichannel analyzer data handling system. A schematic diagram of the improved pulse amplifier and discriminator for photon counting is given. For four-color cluster photometry, the automatic mode gives standard deviations for the color index, in all but the very worst conditions, comparable to those for the manual mode under the best conditions.
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