A fiber-optic three-channel photometer for simultaneous UBVRI measurements - improved design and new results

A modern photometer designed for variable star observation should meet the following specifications: 1. Simultaneous measurements of object, comparison star and sky in order to allow compensation of changing atmospheric transparency and background radiation. 2. Simultaneous multicolor measurements of each channel yielding high efficiency and accurate colors. 3. Coverage of a large wavelength region (U-I) with high time resolution. A photometer, fitting these requirements has been designed at the Universitäts-Sternwarte München. In principle light from three sources in the focal plane of a telescope is guided through optical fibers to three spectrographs, each splitting the incoming signal into five wavelength regions. The resulting 15 output channels are linked to photon counting detectors. Their signals finally are processed in a microcomputer.