SIMBAD references

The combination of variability and proper motion constraints (VPM search) is believed to provide an efficient yet unconventional search strategy for QSOs with selection effects quite different from conventional optical QSO surveys. We performed a VPM QSO search in a 10 square degrees field around M92 on 162 selected digitised Schmidt plates in the Johnson B band with a time-baseline of more than three decades. In Paper I, we constructed a sample of VPM QSO candidates with magnitudes are in the range -21≲M_B≲-29. The statistical properties of the resulting QSO sample are studied in detail. No significant differences were found between our VPM QSO sample and published QSO samples from multicolour or spectroscopic surveys. The fraction of QSOs with unusual colours is estimated to be less than 5 per cent within the magnitude range B≤19.7.