We have modelled radio and far-infrared rotational lines of ^ { 12 } CO and ^ { 13 } CO obtained from the circumstellar envelope of the infrared-bright carbon star IRAS 15194-5115 .
Eleven rotational lines between J =1–0 and 21–20 and nine rotational lines between J =1–0 and 22–21 in the ground vibrational states of ^ { 12 } CO and ^ { 13 } CO , respectively , provide the observational constraints .
A model of the circumstellar envelope with a constant mass-loss rate ( 1 \times 10 ^ { -5 } M _ { \odot } yr ^ { -1 } ) and ^ { 12 } CO/ ^ { 13 } CO-ratio ( 5.5 ) is consistent with our observed FIR and radio data , suggesting that the wind characteristics have not changed significantly over the past few thousand years .
Thus , IRAS 15194-5115 appears to be a highly evolved AGB-star , but the carbon star properties combined with the inferred low ^ { 12 } \mbox { C } / ^ { 13 } \mbox { C } -ratio make the evolutionary status of this star uncertain .
It may have been a J-star for which the ^ { 12 } \mbox { C } / ^ { 13 } \mbox { C } -ratio has remained low , or it may be a star of 5 to 8 solar masses , which has recently become a carbon star due to quenching of hot bottom burning .
The dust properties or the relative amount of dust in the envelope appear to be different from those in the envelope of the well known carbon star IRC+10 216 .