Infrared observations of FG Sagittae in 1993-1997статья
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Аннотация:We present the infrared JHKLM photometry of the peculiar variable FG Sge in 1993-1997. The deep minima observed in the optical light curve of FG Sge since 1992 are shown to result each time from the condensation of a dust layer in the envelope of the star, which is accompanied by a relatively long (~1.5 yr) decline in its mean bolometric luminosity. The amplitude of its pulsations with a period P ~ 115 days remains at the level of the 1980s. The formation of dust embryos, which then rapidly (in ~30 days) grow to sizes ~0.1 microns, takes ~40 days and appears to be concentrated in isolated fragments (clumps, clouds) of the corresponding gaseous layer. As a result, profound dimmings of FG Sge are not accompanied by its appreciable reddening. The subsequent reddening is attributable to the appearance in the envelope of finer dust grains whose mass fraction does not exceed 20%, however. We construct a model for FG Sge as a star of variable luminosity surrounded by a dust envelope in the form of a layer cake with a new dust layer emerging during each deep minimum. This model reproduces the main features of the star's behavior beginning from its first deep minimum in 1992. We show that the dust envelope must contain small (0.05 microns), medium-size (0.1 microns), and large (0.25 microns) graphite grains whose relative number varies with time. The masses of the three dust layers formed in 1992 and 1994 lie within the range (1 - 4) 10^-8 M_solar, and their condensation occurred at a distance of 40-90 R* from the star.