西佛星系
The role of hot dust in the emission from a Seyfert galaxy (Fairall 9) was demonstrated observationally for the first time by Clavel, Wamsteker and Glass in 1989; these observations were modelled theoretically by Barvainis and provided a strong confirmation of the reverberation model for active galactic nuclei. The photometry was part of a multi-year monitoring programme that showed the ubiquity of infrared variability in these objects.