The Abundances of Polyacetylenes Toward CRL618

• Published in: The Astrophysical journal Vol. 728; no. 1; pp. 43 - jQuery1323911264473='48'
• Main Authors: Fonfría, J. P, Cernicharo, J, Richter, M. J, Lacy, J. H
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 10.02.2011; IOP
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; USA, Texas; Vibrational temperature; Line shape; Line identification; stars: AGB and post-AGB; stars: carbon; surveys; Abundance; Column density; Carbon stars; Hydrogen cyanides; Ultraviolet radiation; Circumstellar shells; Rotational temperature; line: profiles; stars: individual (CRL618); line: identification; Asymptotic giant branch
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/728/1/43

We present a mid-infrared high spectral resolution spectrum of CRL618 in the frequency ranges 778-784 and 1227-1249 cm--1 (8.01-8.15 and 12.75-12.85 Delta *mm) taken with the Texas Echelon-cross-Echelle Spectrograph (TEXES) and the Infrared Telescope Facility (IRTF). We have identified more than 170 rovibrational lines arising from C2H2, HCN, C4H2, and C6H2. We have found no unmistakable trace of C8H2. The line profiles display a complex structure suggesting the presence of polyacetylenes in several components of the circumstellar envelope (CSE). We derive total column densities of 2.5 X 1017, 3.1 X 1017, 2.1 X 1017, 9.3 X 1016 cm--2, and 5 X 1016 cm--2 for HCN, C2H2, C4H2, C6H2, and C8H2, respectively. The observations indicate that both the rotational and vibrational temperatures in the innermost CSE depend on the molecule, varying from 100 to 350 K for the rotational temperatures and 100 to 500 K for the vibrational temperatures. Our results support a chemistry in the innermost CSE based on radical-neutral reactions triggered by the intense UV radiation field.