The abundances of polyacetylenes towards CRL618

Abstract

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 um) taken with the Texas Echelon-cross-Echelle Spectrograph (TEXES) and the Infrared Telescope Facility (IRTF). We have identified more than 170 ro-vibrational 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 10^17, 3.1 10^17, 2.1 10^17, 9.3 10^16 cm^-2, and < 5 10^16 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.

9 pages, 4 figures, 1 table; accepted for publication in The Astrophysical Journal

References in corpus (4)

• C${}_{60}$ in Reflection Nebulae
• Formation of fullerenes in H-containing Planetary Nebulae
• A Detailed Analysis of the Dust Formation Zone of IRC+10216 Derived from Mid-IR Bands of C2H2 and HCN
• The Spitzer-IRS spectrum of SMP LMC 11

Cited by in corpus (7)

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• The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations
• The abundance of C2H4 in the circumstellar envelope of IRC+10216
• The abundance of 28Si32S, 29Si32S, 28Si34S, and 30Si32S in the inner layers of the envelope of IRC+10216
• Carbon chemistry in IRC+10216: Infrared detection of diacetylene
• Mapping the Central Region of the PPN CRL 618 at Sub-arcsecond Resolution at 350 GHz
• The maser emitting structure and time variability of the SiS lines J=14-13 and 15-14 in IRC+10216