Infrared spectral evolution of carbon stars

We collected almost all Highly Processed Data Products (HPDP) of ISO SWS01 spectra for the Galactic visual carbon stars, infrared carbon stars, extreme carbon stars and carbon-rich proto-planetary nebulae (PPNs). Those infrared spectra are primarily analyzed and discussed. It is shown that either spectral shapes/peaks, or main molecular/dust features are evidenced to change in the sequence of visual carbon stars, infrared carbon stars, extreme carbon stars and carbon-rich PPNs. Statistically, in this sequence, continua are gradually changed from blue to red and locations of spectral peaks of continua are also gradually changed from short wavelengths to long wavelengths. In addition, in this sequence, intensities of main molecular/dust features are also gradually changed from prominent in the short wavelengths to prominent in the long wavelengths. Furthermore, from 2MASS and IRAS photometric data, the sequence is also proved. Results in this paper strongly support the previous suggestion for the evolution sequence of carbon-rich objects in our Galaxy, that is the sequence of visual carbon stars → infrared carbon stars → extreme carbon stars → carbon-rich PPNs.