The abundance of C{sub 2}H{sub 4} in the circumstellar envelope of IRC+10216
- Grupo de Astrofísica Molecular, Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Inés de la Cruz, 3, Cantoblanco, E-28049, Madrid (Spain)
- National Optical Astronomy Observatory, P.O. Box 26732, Tucson, Arizona, AZ 85726 (United States)
High spectral resolution mid-IR observations of ethylene (C{sub 2}H{sub 4}) toward the AGB star IRC+10216 were obtained using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). 80 ro-vibrational lines from the 10.5 μm vibrational mode ν{sub 7} with J ≲ 30 were detected in absorption. The observed lines are divided into two groups with rotational temperatures of 105 and 400 K (warm and hot lines). The warm lines peak at ≃ −14 km s{sup −1} with respect to the systemic velocity, suggesting that they are mostly formed outwards from ≃20R{sub ⋆}. The hot lines are centered at −10 km s{sup −1} indicating that they come from a shell between 10 and 20R{sub ⋆}. 35% of the observed lines are unblended and can be fitted with a code developed to model the emission of a spherically symmetric circumstellar envelope. The analysis of several scenarios reveals that the C{sub 2}H{sub 4} abundance relative to H{sub 2} in the range 5−20R{sub ⋆} is 6.9×10{sup −8} on average and it could be as high as 1.1 × 10{sup −7}. Beyond 20R{sub ⋆}, it is 8.2 × 10{sup −8}. The total column density is (6.5 ± 3.0) × 10{sup 15} cm{sup −2}. C{sub 2}H{sub 4} is found to be rotationally under local thermodynamical equilibrium (LTE) and vibrationally out of LTE. One of the scenarios that best reproduce the observations suggests that up to 25% of the C{sub 2}H{sub 4} molecules at 20R{sub ⋆} could condense onto dust grains. This possible depletion would not significantly influence the gas acceleration although it could play a role in the surface chemistry on the dust grains.
- OSTI ID:
- 22869437
- Journal Information:
- Astrophysical Journal, Vol. 835, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Acetylene bands observed in carbon stars: a laboratory study and an illustrative example of its application to IRC+10216
Circumstellar envelope of IRC+10216