Some Experiments with an Sec Image Tube for High Precision Multi-Colour Photometry of Galactic Clusters

Abstract

The possibility of high precision multi-colour stellar photometry with an SEC vidicon camera is studied on the galactic cluster NGC 581, In particular, the best exploitation of calibration information is sought. The correlation length is determined and used for data compression. Several calibration techniques are discussed and the best one is selected and tested. A related problem of zero level is examined. In order to reduce the number of necessary calibration measurements, a separation of the SEC target non linearity and the photocathode quantum efficiency local dependency is carried out. Certain incompatibilities in calibrated data are found. Nevertheless, the magnitude of some stars already measured in the Geneva system is presented, and sources of error are discussed.