Herschel/HIFI observation of highly excited rotational lines of HNC toward IRC +10 216

Abstract

We report the detection in emission of various highly excited rotational transitions of HNC (J = 6-5 through J =12-11) toward the carbon-star envelope IRC +10 216 using the HIFI instrument on-board the Herschel Space Observatory. Observations of the J = 1-0 and J = 3-2 lines of HNC with the IRAM 30-m telescope are also presented. The lines observed with HIFI have upper level energies corresponding to temperatures between 90 and 340 degrees Kelvin, and trace a warm and smaller circumstellar region than that seen in the interferometric maps of the J = 1-0 transition, whose emission extends up to a radius of 20". After a detailed chemical and radiative transfer modeling, we find that the presence of HNC in the circumstellar envelope of IRC +10 216 is consistent with formation from the precursor ion HCNH+, which in turn is produced through several proton transfer reactions which are triggered by the cosmic-ray ionization. We also find that the radiative pumping through 21 um photons to the first excited state of the bending mode v2 plays a crucial role to populate the high-J HNC levels involved in the transitions observed with HIFI. Emission in these high-J rotational transitions of HNC is expected to be strong in regions which are warm and dense and/or have an intense infrared flux at wavelengths around 21 um.

References in corpus (5)

• Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216
• A Detailed Analysis of the Dust Formation Zone of IRC+10216 Derived from Mid-IR Bands of C2H2 and HCN
• Density-enhanced gas and dust shells in a new chemical model for IRC+10216
• Detection of HNC and tentative detection of CN at z=3.9
• Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS

Cited by in corpus (11)

• The growth of carbon chains in IRC+10216 mapped with ALMA
• Unveiling the dust nucleation zone of IRC+10216 with ALMA
• Discovery of Time Variation of the Intensity of Molecular Lines in IRC+10216 in The Submillimeter and Far Infrared Domains
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• The abundance of 28Si32S, 29Si32S, 28Si34S, and 30Si32S in the inner layers of the envelope of IRC+10216
• The surprisingly carbon-rich environment of the S-type star W Aql
• Charting Circumstellar Chemistry of Carbon-rich AGB Stars: I. ALMA 3 mm spectral surveys
• Herschel/HIFI search for H2-17O and H2-18O in IRC+10216: constraints on models for the origin of water vapor
• Multi-line study of the radial extent of SiO, CS, and SiS in AGB envelopes
• The spectra of evolved stars at 20--25\,GHz: tracing circumstellar chemistry during the asymptotic giant branch to planetary nebula transition
• Exploring circumstellar chemistry in X-ray emitting AGB stars