1996A&A...306..391A

Deep optical VRI images and multi-frequency (1.7, 5.0, 8.4 and 22GHz) VLBI observations of 0646+600, a prototype OQQ, show that it is a `red' and variable quasar with a compact mas double/triple radio structure, which exhibits anomalous structural changes. Between 1989.79 and 1992.22, the overall separation of the two bright components at 5 GHz decreased by ∼0.25mas, and a weak middle feature evident in 1989 was not detected in the later observations. These components also appear to exhibit a frequency dependent separation. 0646+600 thus joins 4C39.25 as the second radio source in which apparent angular size contraction is detected. We discuss both these structural changes in 0646+600.