1997A&A...327..636M

This is the first time that CCD-photometry in the three filter {DELTA}a system (Maitzen, 1976A&A....51..223M) was carried out after two decades of classical photoelectric photometry. The aim is to extend the successful search for chemically peculiar stars to more and distant open clusters as well as far galactic fields. In this paper we present CCD-photometry for a sample of 25 field stars with published spectroscopic peculiarity types. 22 of them show discordance between their Michigan catalogue types (non-peculiar) and the Bidelman & MacConnell (1973AJ.....78..687B; BC) peculiarity assignments. Eight stars are peculiar in {DELTA}a (five of them also in the Geneva index {DELTA}(V1-G)) thus supporting BC, mainly among their Silicon star discoveries. Considering cases where Silicon line enhancements were interpreted as peculiar instead as indicator of higher luminosity by BC, and the perfect detection of the three unambiguous peculiar stars, in addition to the achievement of an accuracy of 0.003mags, we are justified to conclude that the performance of our CCD-{DELTA}a photometry perfectly matches the requirements of the conventional photometric technique and thus opens the way to observations of fainter stars.