Δa and Strömgren photometry of stars in the Renson-catalogue of Ap and Am stars

Abstract

We have observed 131 stars of Renson's (1991) catalogue of Ap and Am stars both in the Stromgren & Maitzen's (1976) Δa system as a contribution to the photometric studies of the λ5200 broad band flux depression feature in chemically peculiar stars. With few exceptions the probability grouping of Renson for membership in the CP2 group of peculiar stars is nicely reflected by peculiar values of Δa. Comparison with already available Δa values yields slightly larger values due to a minor shift in the filter g1 sampling the depression. As found by Maitzen & Vogt (1983) the Geneva system peculiarity parameters correlate well with Δa. This study demonstrates the advantageous performance of a photoelectric photometer with a rapidly rotating filter wheel moving in a stop and go mode.