1. We have provided Strömgren and 
values for a sample of 131 stars
in the Renson (1991) catalogue of Ap and Am stars. While 84
percent of the stars have already been measured in the Strömgren system,
only 10 percent have previous measurements in .
The average deviations from published Strömgren photometry are
comparable to the published accuracy with the exception of very few
cases which could be ascribed to intrinsic variability, and in one
case (HD 209711) where we are suspicious about a typographical error.
photometry agrees well with previously published values, but has
a slight tendency for enhanced due to the position of the g2 filter.
Only the synthetic values of Lebedev (1986) for 3 CP3 stars
in common are systematically too large.
2. Renson's (1991) assignment of peculiarity probability is in
excellent agreement with our results for the magnetic peculiar stars,
i.e. CP2. The behaviour of 2 rather probable Ap stars which show
non-peculiar is an exception to this situation. Further observations may
clear up the question, whether variability could be responsible.
3. This study has confirmed with a sufficiently large data base
that CP1 stars are
photometrically normal in the system with the exception of very
few stars close to the 3
threshold and one star, HD 196655,
which may be a CP2 star.
We have found one CP4 star to be peculiar in , and one CP3 object
just at the threshold.
4. In very good accord with the results of Maitzen & Vogt
(1983) Geneva photometry is helpful with parallel results on
photometric peculiarity. Especially we have to outline that there was no
case among the CP2 group where photometric peculiarity was found in the
Geneva system and not in .
5. Finally, we have to emphasize that our results have been obtained at the required level of accuracy which was possible only through the use of a non-classical photoelectric technique in an astroclimate (central Europe), which is rather different from excellence.
Acknowledgements
Our thanks go to Dr. M. Stoll who kindly provided software and hardware for the photometer and the telescope control system used in this work. We express special gratitude to Mrs. E. Pressberger for her untiring assistance during the observations. The project was supported by the Hochschuljubiläumsstiftung der Stadt Wien (to HMM, under Wiener Zweikanalphotometer). EP acknowledges support of this research within the working group Asteroseismology-AMS with funding from the Fonds zur Förderung der wissenschaftlichen Forschung (project S7303-AST). Use was made of the Simbad database, operated at CDS, Strasbourg, France.