2007/09/30 by J. P. Fonfría, J. Cernicharo, Matthew J. Richter +2 · 1 citation
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Spectroscopy and Laser Applications #astro-ph
paper · pdf · doi:10.1086/523882
8 pages, 16 figures, 2 machine-readable tables, accepted in the Astrophysical Journal
arxiv created 2007/10/09 · openalex publication_date 2008/01/16 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/30
A spectral survey of IRC +10216 has been carried out in the range 11-14 μm with a spectral resolution of about 4 km s −1 . We have identified a forest of lines in six bands of C 2 H 2 involving the vibrational states from the ground to 3ν 5 and in two bands of HCN, involving the vibrational states from the ground up to 2ν 2 . Some of these transitions are observed also in H 13 CCH and H 13 CN. We have estimated the kinetic, vibrational, and rotational temperatures and the abundances and column densities of C 2 H 2 and HCN between 1 R * and 300 R * (≃1.5 × 10 16 cm) by fitting about 300 of these rovibrational lines. The envelope can be divided into three regions with approximate boundaries at 0.019″ (the stellar photosphere), 0.1″ (the inner dust formation zone), and 0.4″ (outer dust formation zone). Most of the lines might require a large microturbulence broadening. The derived abundances of C 2 H 2 and HCN increase by factors of 10 and 4, respectively, from the innermost envelope outward. The derived column densities for both C 2 H 2 and HCN are ≃1.6 × 10 19 cm −2 . Vibrational states up to 3000 K above ground are populated, suggesting pumping by near-infrared radiation from the star and innermost envelope. Low rotational levels can be considered under LTE, while those with J > 20–30 are not thermalized. A few lines require special analysis to deal with effects like overlap with lines of other molecules.