The infrared temporal evolution of FG Sagittae

We present near- and mid-infrared photometry of the post-AGB star FG Sge obtained at two distinct epochs separated by a period of 10 years. Observations of FG Sge taken in 1983 suggest that the 1 to 12 μm energy distribution was produced at that time by a stellar photosphere, with a blackbody temperature of ≈5600 K. In late August of 1992, FG Sge exhibited a marked decline (≈3 mag in V) in its visible light curve. At the same time the 1 to 18.0 μm infrared energy distribution has evolved to become a ≈1000 K blackbody. We propose that this light decline partially is due to the ejection and condensation of a dust shell. We estimate the amount of dust condensed during this episode to be ≈3.3 × 10^-9 M_⊙, with a covering factor (total visual depth) of ≈0.3.