SIMBAD references

Normal J-type carbon stars without silicate features have been modelled, considering two kinds of grains simultaneously: amorphous carbon (A.C.) and silicon carbide (SiC). The temperature of central stars and some characteristics of circumstellar shell as extinction opacities and its extension were determined by fitting the flux curves. The SiC/A.C. ratio as well as the energy distributions and temperature law have been studied. The results show that these J-type carbon stars have thin envelopes (with extinction opacities about 0.02) and intermediate SiC/A.C. ratios. Based on these results two alternative scenarios are discussed: (1) Normal J-type carbon stars would be in an intermediate group between Groups I and II introduced by Lorenz-Martins & Lefevre (1994). (2) J-type stars (normal and peculiar) could form an alternative evolutive sequence, which differs from that proposed for ordinary carbon stars.