Aperture photometry at the Unisa observatory; system evaluation via light curves of eclipsing binaries

Abstract

The University of South Africa has built a small observatory for teaching and research. The 35cm Schmidt-Cassegrain reflector and the SSP-5A photometer with Johnson UBV filters were used to evaluate the local possibilities for aperture photometry. Extinction and transformation coefficients and zero points were determined with the RPHOT software package from standard star photometry. To determine the system limits, UBV light curves were obtained for four eclipsing binaries, ranging between magnitudes 7 and 13. In B the limit is 12,5, in U it is 12,0 and in V only 11,0 with large scatter even for bright objects. The rapidly varying sky background in an urban site may be a major cause. A related problem is the large, fixed photometer diaphragm, aggravating the bright sky situation. Possible solutions to this and other problems were suggested. The system can be used fruitfully, especially for single filter photometry of periodic and nonperiodic variables.