A 1.3 cm line survey toward IRC +10216

Abstract

IRC +10216 is the prototypical carbon star exhibiting an extended molecular circumstellar envelope. Its spectral properties are therefore the template for an entire class of objects. The main goal is to systematically study the $\lambda$ $\sim$1.3 cm spectral line characteristics of IRC +10216. We carried out a spectral line survey with the Effelsberg-100 m telescope toward IRC +10216. It covers the frequency range between 17.8 GHz and 26.3 GHz (K-band). In the circumstellar shell of IRC +10216, we find 78 spectral lines, among which 12 remain unidentified. The identified lines are assigned to 18 different molecules and radicals. A total of 23 lines from species known to exist in this envelope are detected for the first time outside the Solar System and there are additional 20 lines first detected in IRC +10216. The potential orgin of "U" lines is also discussed. Assuming local thermodynamic equilibrium (LTE), we then determine rotational temperatures and column densities of 17 detected molecules. Molecular abundances relative to H${}_2$ are also estimated. A non-LTE analysis of NH${}_3$ shows that the bulk of its emission arises from the inner envelope with a kinetic temperature of 70$\pm$20 K. Evidence for NH${}_3$ emitting gas with higher kinetic temperature is also obtained, and potential abundance differences between various ${}^{13}$C-bearing isotopologues of HC${}_5$N are evaluated. Overall, the isotopic ${}^{12}$C/${}^{13}$C ratio is estimated to be 49$\pm$9. Finally, a comparison of detected molecules in the $\lambda$ $\sim$1.3 cm range with the dark cloud TMC-1 indicates that silicate-bearing molecules are more predominant in IRC +10216.

32 pages, 9 figures, Accepted by A&A

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• High-resolution wide-band Fast Fourier Transform spectrometers
• New molecules in IRC+10216: confirmation of C${}_5$S and tentative identification of MgCCH, NCCP, and SiH${}_3$CN
• Detection of circumstellar CH2CHCN, CH2CN, CH3CCH and H2CS
• Density-enhanced gas and dust shells in a new chemical model for IRC+10216
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• The detection of the (J,K)=(18,18) line of NH3
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• Molecules in the carbon-rich protoplanetary nebula CRL 2688
• Constraining stellar parameters and atmospheric dynamics of the carbon AGB star V Oph
• Charting Circumstellar Chemistry of Carbon-rich AGB Stars: I. ALMA 3 mm spectral surveys
• Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde V. The massive filament DR21
• Searching for further evidence for cloud-cloud collisions in L1188
• 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
• Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars. II. Abundances and spatial distributions of CS
• New submillimetre HCN lasers in carbon-rich evolved stars