A set of self-consistent model calculations of the evolution from visual carbon stars to infrared carbon stars is presented. A two-shell system model, the interrupted mass-loss model (oxygen-rich detached shell and newly forming SiC dust shell), has been developed. This model overcomes the shortcomings of the single detached-shell model (Chan and Kwok 1988) and the SiC shell model (Chan and Kwok 1990). A new mass-loss formula, which describes the gradually increasing mass-loss rate at the early stage of the infrared carbon stars, is introduced to simulate the effect of the newly forming SiC shell. The model tracks successfully explain a ''C''-shaped distribution of carbon stars in the color-color diagram. The energy distributions of approximately 110 transition objects are fitted with developing SiC dust shells using the interrupted mass-loss model. The existence of these transition objects with infrared properties intermediate between visual and infrared carbon stars, lends further support to the idea of an evolutionary link between visual and infrared carbon stars.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC
