The Analysis Of ISO SWS Spectra And The Studies Of Molecular And Dust Features For 29 SiC Carbon Stars

This present paper is contributed to the study of the evolutionary nature of ISO SWS spectra from carbon-rich AGB stars (carbon stars) and molecular and dust features around such carbon stars. Carbon stars with C/O >1 are a kind of stars that form at the AGB stage and evolved from oxygen-rich AGB stars with mid-mass. Because the photospheric temperature of carbon stars are less than 3000K and the temperature of rich-dust envelope formed by the mass loss is lower, and therefore most of the energy from carbon stars are radiated between 1 to 60um range, in which the vibrational and ro-vibrational bands of many molecules also lies, the study of infrared spectra in this wavelength range is very important to reveal chemical compositions, dust formation process, the atmospheric structure and evolutionary status of stars.Usually, carbon stars can be divided into three groups: Visual carbon stars, Infrared carbon stars and Extreme carbon stars. Visual carbon stars whose mid-infrared spectra are mainly dominated by photospheric continuum and show large excesses at 60um, represent a transition phase which follows an interruption of mass loss from the oxygen-rich phase and begins a new phase of the mass loss of carbon-rich material. Excesses at 60um in these stars are the emission from the residual of oxygen-rich material. The infrared carbon stars, whose infrared spectra are mainly due to the dust emission in the circumstellar envelope, are usually believed to be surrounded by the carbon rich envelope characterized by the SiC emission feature at 11.3um. These stars are undergoing important mass loss process and are likely to represent a more evolved phase of the stellar evolution than visual carbon stars. The extreme carbon stars, whose derived mass loss rates and optical depths are both very high, are more evolved than infrared carbon stars. These stars are expected to evolveinto protoplanatary nebula soon.We have elected 29 carbon stars with SiC emission feature at 11.3um, i.e. SiC carbon stars, which include Visual carbon stars, Infrared carbon stars and Extreme carbon stars to be our working samples in this paper. By using the ISO SWS spectra we have studied their physical nature including their molecular and dust features in the circumstellar envelope to make us understand the evolutionary status of carbon stars. After competing our work, some conclusions expected are obtained for the evolutionary principles of carbon stars and the evolutionary nature of molecule and dust features around them.