Silicon in the dust formation zone of IRC +10216 as observed with PACS and SPIRE on board Herschel

Abstract

The interstellar medium is enriched primarily by matter ejected from evolved low and intermediate mass stars. The outflows from these stars create a circumstellar envelope in which a rich gas-phase and dust-nucleation chemistry takes place. We observed the nearest carbon-rich evolved star, IRC+10216, using the PACS (55-210 μm) and SPIRE (194-672 μm) spectrometers on board Herschel. We find several tens of lines from SiS and SiO, including lines from the v=1 vibrational level. For SiS these transitions range up to J=124-123, corresponding to energies around 6700K, while the highest detectable transition is J=90-89 for SiO, which corresponds to an energy around 8400K. Both species trace the dust formation zone of IRC+10216, and the broad energy ranges involved in their detected transitions permit us to derive the physical properties of the gas and the particular zone in which each species has been formed. This allows us to check the accuracy of chemical thermodynamical equilibrium models and the suggested depletion of SiS and SiO due to accretion onto dust grains.

arXiv comment5 pages, 3 figures, 7 pages in online appendix, Astronomy & Astrophysics in press

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• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
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• ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
• A high resolution line survey of IRC+10216 with Herschel. First results: Detection of warm silicon dicarbide SiC2
• Discovery of Time Variation of the Intensity of Molecular Lines in IRC+10216 in The Submillimeter and Far Infrared Domains
• Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS
• Detection of anhydrous hydrochloric acid, HCl, in IRC+10216 with the Herschel SPIRE and PACS spectrometers
• Water in IRC+10216: a genuine formation process by shock-induced chemistry in the inner wind
• On the physical structure of IRC+10216. Ground-based and Herschel observations of CO and CCH
• Study of CS, SiO, and SiS abundances in carbon star envelopes: Assessing their role as gas-phase precursors of dust
• 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
• Late Stages of Stellar Evolution - Herschel's contributions
• Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes -- I. The case of hydrogen cyanide
• On the nature of the enigmatic object IRAS 19312+1950: A rare phase of massive star formation?
• The chemistry of extragalactic carbon stars
• The Role of Ultraviolet Photons in Circumstellar Astrochemistry
• Herschel/HIFI search for H2-17O and H2-18O in IRC+10216: constraints on models for the origin of water vapor
• Warm CO in evolved stars from the THROES catalogue. II. Herschel/PACS spectroscopy of C-rich envelopes
• The Herschel SPIRE Fourier Transform Spectrometer Spectral Feature Finder III. Line Identification and Off-Axis Spectra
• The Significant Role of Hydrogen in the Formation of Silicon Carbide in Evolved Stars