Abstract:
A high speed multicolour stellar photometer system has been designed and partially constructed. Microprocessors control data acquisition and recording as well as supervising the correct operation of the system. The photometer head was designed for use with Cassegrain telescopes of about 50cm aperture.
A survey of photodetectors and photodetection techniques established that photon counting using photomultipliers is the optimum high speed technique for the spectral region of interest (3500-6500Å). Criteria for selection of a suitable photomultiplier are established. Several amplifiers and discriminators suitable for photon counting were developed together with a high speed comparator suitable for use in a discriminator. Input pulse-derandomisers and synchronised counter gating techniques circumvent the limitations imposed by conventional counter gating techniques.
The photometer head incorporates several novel features including a linear brightness illumination system, and continuous monitoring of slide mirror, flip mirror, and darkslide positions. Field tests of the photometer head have shown that it is both easy to operate and performs reliably when it is used to measure stars within the range of brightness from 5th to 15th visual magnitude.