Comparison star sequences for optical photometry of active galactic nuclei and quasars

As part of a campaign to monitor 23 quasars and Seyfert 1 galaxies on timescales of minutes to a few months, we obtained broadband relative photometry of more than 140 different "comparison" stars. We attained typical 1 sigma flux uncertainties of 2% through differential photometry of field stars in the same CCD frames as the active galactic nuclei (AGNs). These stars form i-band (lambda (eff) similar to 0.7 mum), yellow (0.59 mum), and blue (0.45 mum) photometric sequences for the further monitoring of these AGNs. For about half these fields, we use absolute photometry to calibrate the relative magnitudes. Finding charts, filter prescriptions, comparison star relative photometry, and some tentative variable star identifications are presented. Also included are the foundations of the AGN photometry, which appears in a companion paper in The Astrophysical Journal.