4 Summary

In this paper we present accurate photometry (V Johnson and RI Cousins) for 50 stars, in the fields of 12 bright Seyfert 1 galaxies, suitable for calibration purposes in obtaining differential photometry and therefore for variability studies. These stars are brighter than $16^{\rm m}$ and are located at distances smaller than $6\hbox{$^\prime$ }$ from the AGN. The accuracy of our photometry is $0\hbox{$.\!\!^{\rm m}$ }03 - 0\hbox{$.\!\!^{\rm m}$ }06$. Finding charts for all stars and AGNs are given. We hope that these standards could be useful for optical monitoring of Seyfert galaxies that could be performed successfully even with telescopes with diameter of the mirror 0.5 - 1.0-m.

Acknowledgements

We thank G.T. Petrov for inspiring this work, B. Mihov for useful discussions and help in preparation of the manuscript, and P. Lampens for general comments. We also thank the anonymous referee for his useful suggestions that improved much this paper. CCD ST-8 at the Observatory of Belogradchik is provided by Alexander von Humboldt foundation, Germany. The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166.