David Deming

CN and HCN in the infrared spectrum of IRC + 10216

The abundance of HCN in the inner circumstellar shell of IRC + 10216 has been remeasured using the 12-micron nu2 band. The 12-micron lines are less saturated than HCN 3-micron lines previously detected in the spectrum of IRC + 10216. The observed 12-micron HCN line is formed in the circumstellar shell from about 4 to 12 R{sub {asterisk}} in accord with a photospheric origin for HCN. The derived HCN abundance in the 4 to 12 R{sub {asterisk}} region is 4 {times} 10{sup {minus}5} and the column density is 7 {times} 10{sup 18}/sq cm. The 5-micron CN vibration-rotation fundamental band was detected for the first time in an astronomical source. Using four CN lines, the CN column density was determined to be 2.6 {times} 10{sup 15}/sq cm and the rotational temperature to be 8 {plus minus} 2 K. The peal radial abundance is 1 {times} 10{sup {minus}5}. The values for the temperature and abundance are in good agreement with microwave results and with the formation of CN from the photolysis of HCN. 30 refs.