MODELS OF THE OPTICALLY THIN DUST SHELLS OF CARBON STARS

The models of hot optically thin dust shells surrounding a carbon star and consisting of amorphous carbon dust particles are calculated. The color indices, the surface brightness distributions, and the one-dime nsional brightness distributions in the near-IR are evaluated. It is s hown that an optically thin dust shell surrounding a carbon star can b e observed as a bright annulus characterized by a sharp maximum in bri ghtness. The radius of the annulus coincides both with the inner bound ary of the dust shell and with the boundary of the grain-forming regio n. The modem methods of the high resolving power allow the hot dust sh ell to be detected provided that the optical depth in the near-IR is l arger than approximately 0.05 and the angular resolution is better tha n the angular radius of the star. The model two-color diagrams and, es pecially, IRAS two-color diagrams are analyzed.