The fading of the Seyfert galaxy F-9.

In view of the amplitude of its H-beta variation, the Seyfert galaxy F-9 is one of the most strongly variable known. Most of this change occurred within the last three years, and has taken the classification of F-9 from that of a very strong Seyfert 1 to nearly Seyfert 2 status. The continuum, broad emission, and Fe II lines are noted to vary in relation to one another, and may be quantitatively understood in terms of recent, detailed photoionization calculations.