The development of a steady state, asymptotic giant branch type, circumstellar wind around the "born again" star FG sagittae

We report the results of a 20 year campaign to monitor the infrared (IR) spectral energy distribution (SED) of the "born again" star FG Sge, which is embedded in an old planetary nebula. The IR data show that the central star apparently reestablished an essentially steady state post-asymptotic giant branch (AGB) type wind in late 1992. Since then, the visual light curve has shown irregular large amplitude variations on timescales of 200-400 days, while the IR SED has maintained a constant luminosity. The IR SED has been dominated by thermal emission from carbon dust at a temperature of ≃ 1000 K for nearly 10 years. The thermal emission is primarily from grains forming in the 1000 K condensation zone at the base of the outflow. The wind appears to be optically thick in the visual, and the central engine may be undergoing episodes of pulsational activity that cause the visual optical depth of the wind to vary. The central engine appears to be cooling steadily at constant luminosity. We estimate the mass-loss rate of the FG Sge wind to be between 2.3 × 10^-5 and 1.2 × 10^-4 M_⊙ yr ^-1 as would be expected for a star rejoining the tip of the AGB.