On the nature of carbon stars with the promise of FIRST

A set of self-consistent model calculations of the evolution from visual carbon stars to infrared carbon stars is presented and reviewed. A two-shell system model, the interrupted mass-loss model, has been developed. A revised 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 colour-colour diagram. 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. FIRST mission will be played an important role or the detailed study of the nature of carbon stars.