On the completeness of a sample of bright quasars selected by colour excess in the direction of the North Galactic Pole

The Medium Bright Quasar survey (MBQS) shows evidence for a dearth of bright quasars in a Palomar Schmidt field centred on Selected Area (SA) 57 near the North Galactic Pole, compared to similar fields centred on SA 28, 29, 55, and 94. The SA 57 field has been searched again for bright quasar candidates with the help of a second survey plate exposed according to a slightly modified Haro–Luyten three-colour (Tonantzintla) prescription. Candidates so selected have both a blue and ultraviolet excess (B–UVX). All objects that were selected previously were re-selected to the limit of the MBQS. Only one bright B–UVX object (the star HZ 42) had been missed in the original survey. Five new objects judged within the photometric errors to have the highest probability of being B–UVX objects, were examined spectroscopically. They were found to be stars. The main result of the paper is that there appear to be no B–UVX quasars in the SA 57 field that are brighter than B = 17.25 mag. The significance of this apparent anomaly is briefly discussed.