The Abundance of C 2 H 4 in the Circumstellar Envelope of IRC+10216

• Published in: The Astrophysical journal 2017-02, Vol.835 (2), p.196
• Main Authors: Fonfría, J P, Hinkle, K H, Cernicharo, J, Richter, M J, Agúndez, M, Wallace, L
• Format: Article
• Language: English
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/835/2/196

High spectral resolution mid-IR observations of ethylene (C H ) towards the AGB star IRC+10216 were obtained using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Eighty ro-vibrational lines from the 10.5 m vibrational mode with ≲ 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 with respect to the systemic velocity, suggesting that they are mostly formed outwards from ≃ 20 . The hot lines are centered at -10 km s indicating that they come from a shell between 10 and 20 . 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 reveal that the C H abundance relative to H in the range 5 - 20 is 6.9 × 10 in average and it could be as high as 1.1 × 10 . Beyond 20 , it is 8.2 × 10 . The total column density is (6.5 ± 3.0) × 10 cm . C H 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 H molecules at 20 could condense onto dust grains. This possible depletion would not influence significantly the gas acceleration although it could play a role in the surface chemistry on the dust grains.