A QSO survey via optical variability and zero proper motion in the M 92 field

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 M 92 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 $B\le19.7$. The spectroscopic follow-up observations revealed 58 QSOs and 7 Seyfert 1 galaxies as well as 27 narrow-emission line galaxies. We present the low-resolution spectra and the data for the QSOs and Seyfert galaxies: AGN types, accurate positions, redshifts, mean B magnitudes, and colour indices, along with the selection parameters of the VPM search, i.e., indices for variability, proper motion, and image structure. The redshifts cover the interval $0 \la z \la 3$; absolute magnitudes are in the range $-21 \la M_{B} \la -29$. 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 $B \le 19.7$