Revisiting old (AGN) friends -- what's changed in their spectral looks
  Active Galactic Nuclei (AGN) have long been known to be variable, but the
amplitude, timescale and nature of these changes can often differ dramatically
from object to object. The richest source of information about the properties
of AGN and the physical processes driving these remains the optical spectrum.
While this spectrum has remained remarkably steady over decades for some AGN,
other objects, referred to as Changing Look AGN, have experienced a
comprehensive spectral transformation. Developments in the detection technology
have enabled detailed probing in other wavebands, highlighting for example
often quite different variability patterns for high energy emission. This paper
explores the current characteristics of some long-known (and almost forgotten)
Seyfert galaxies. It compares their present optical spectral properties,
determined from recent observations at the South African Astronomical
Observatory, with those from much earlier epochs. It furthermore considers the
implication of the changes that have taken place, alternatively the endurance
of specific spectral features, on our understanding of the mechanisms of the
observed targets in particular, and on AGN models in general.
