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We present the first speckle interferometric observations of R CrB, theprototype of a class of peculiar stars which undergo irregular declines intheir visible light curves. The observations were carried out with the 6mtelescope at the Special Astrophysical Observatory near maximum light (V=7,1996 Oct. 1) and at minimum light (V=10.61, 1999 Sep. 28). A spatial resolutionof 75mas was achieved in the K-band. The dust shell around R CrB is partiallyresolved, and the visibility is approximately 0.8 at a spatial frequency of 10cycles/arcsec. The two-dimensional power spectra obtained at both epochs do notshow any significant deviation from circular symmetry. The visibility functionand spectral energy distribution obtained near maximum light can besimultaneously fitted with a model consisting of the central star and anoptically thin dust shell with density proportional to r^-2. The inner boundaryof the shell is found to be 82Rstar (19mas) with a temperature of 920K.However, this simple model fails to simultaneously reproduce the visibility andspectral energy distribution obtained at minimum light. We show that thisdiscrepancy can be attributed to thermal emission from a newly formed dustcloud.

Diffraction-limited speckle interferometry and modeling of the circumstellar envelope of R CrB at maximum and minimum light