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Published online by Cambridge University Press: 12 April 2016
Application of the homogeneous nucleation theory to the problem of R CrB stars shows that the radial distance of the inner boundary of the carbon supersaturation region is at about 12 photospheric radii for a stellar effective temperature Te = 6000 K. Formation of an optically thick dust shell becomes possible at mass loss rates Ṁ ≳ 10−6 M⊙/yr. However, the upper limit of this mass loss rate cannot considerably exceed 10−5 M⊙/yr since, at higher Ṁ, the theoretically predicted rate of the visual brightness decline is larger than that derived from observations. Comparison of the theoretically predicted radii of dust grains with those observed in R CrB and RY Sgr shows that the mass loss rate in these stars should be in the range of 1 × 10−7 M⊙/yr to 3 × 10−6 M⊙/yr.