3C 345: the historical light curve (1967-1990) from the digitized plates of the Asiago Observatory

As part of a large project to digitize the plate archives of the Italian and Vatican Astronomical Observatories, we have already performed the digitization of all available plates of the field of the quasar 3C 345. The plates, approximately 100 in number, were taken with the three telescopes of the Asiago Observatory (122 cm, 182 cm, 67/90 cm Schmidt Telescope) in the period from 1967 to 1990. We present here essentially new data, mostly in the B band, about the variability of 3C 345 and also of four other objects (three quasars - Q1, Q2 and Q3 - and the active galaxy NGC 6212) in the same field, in that period. Beyond the well-known 3C 345 itself, the other three quasars also show variability, with a range of 2.0 mag for Q1 and Q2, and 1 mag for Q3. The low-level variability detected for the nucleus of NGC 6212 is more doubtful, and should be confirmed by linear detector data.