A Molecular Line Survey of the Highly Evolved Carbon Star CIT 6

Abstract

We present a spectral line survey of the C-rich envelope CIT 6 in the 2mm and 1.3mm bands carried out with the Arizona Radio Observatory (ARO) 12m telescope and the Heinrich Hertz Submillimeter Telescope (SMT). The observations cover the frequency ranges of 131--160 GHz, 219--244 GHz, and 252--268 GHz with typical sensitivity limit of T_R<10 mK. A total of 74 individual emission features are detected, of which 69 are identified to arise from 21 molecular species and isotopologues, with 5 faint lines remaining unidentified. Two new molecules (C4H and CH3CN) and seven new isotopologues (C17O, 29SiC2, 29SiO, 30SiO, 13CS, C33S, and CS) are detected in this object for the first time. The column densities, excitation temperatures, and fractional abundances of the detected molecules are determined using rotation diagram analysis. Comparison of the spectra of CIT 6 to that of IRC+10216 suggests that the spectral properties of CIT 6 are generally consistent with those of IRC+10216. For most of the molecular species, the intensity ratios of the lines detected in the two objects are in good agreement with each other. Nevertheless, there is evidence suggesting enhanced emission from CN and HC3N and depleted emission from HCN, SiS, and C4H in CIT 6. Based on their far-IR spectra, we find that CIT 6 probably has a lower dust-to-molecular gas ratio than IRC+10216. To investigate the chemical evolution of evolved stars, we compare the molecular abundances in the AGB envelopes CIT 6 and IRC+10216 and those in the bright proto-planetary nebula CRL 618. The implication on the circumstellar chemistry is discussed.

39 pages, 9 figures, accepted for publication in ApJ

References in corpus (4)

• Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216
• A spectral line survey in the 2 mm and 1.3 mm windows toward the carbon rich envelope of IRC +10216
• The abundance of SiS in circumstellar envelopes around AGB stars
• Molecular survey of CRL618

Cited by in corpus (17)

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• Evidence of a Binary-Induced Spiral from an Incomplete Ring Pattern of CIT 6
• A molecular line survey of the extreme carbon star CRL 3068 at millimeter wavelengths
• Radio Stars: from kHz to THz
• Tracing the asymmetry in the envelope around the carbon star CIT 6
• Silicon isotopic abundance toward evolved stars and its application for presolar grains
• A Molecular Line Survey of the Carbon-Rich Proto-Planetary Nebula AFGL 2688 in the 3mm and 1.3mm Windows
• The astrosphere of the Asymptotic Giant Branch star CIT 6
• Molecular gas in 21 and 30 micron sources: the 2\,mm and 1.3\,mm spectra of IRAS\,21318+5631 and 22272+5435
• PACS and SPIRE range spectroscopy of cool, evolved stars
• Small carbon chains in circumstellar envelopes
• The spectra of evolved stars at 20--25\,GHz: tracing circumstellar chemistry during the asymptotic giant branch to planetary nebula transition
• A 3 mm Molecular Line Survey toward The C-star Envelope CIT 6
• Interrelations between Astrochemistry and Galactic Dynamics
• The Abundance of SiC${}_2$ in Carbon Star Envelopes