Si-bearing molecules towards IRC+10216: ALMA unveils the molecular envelope of CWLeo

Abstract

We report the detection during the ALMA Cycle 0 of SiS rotational lines in high-vibrational states as well as SiO and SiC${}_2$ lines in their ground vibrational state, towards IRC+10216. The spatial distribution of these molecules shows compact emission for SiS and a more extended emission for SiO and SiC${}_2$, and also proves the existence of an increase in the SiC${}_2$ emission at the outer shells of the circumstellar envelope. We analyze the excitation conditions of the vibrationally excited SiS using the population diagram technique and we used a large velocity gradient model to compare with the observations. We found moderate discrepancies between the observations and the models that could be explained if SiS lines detected are optically thick. Additionally, the line profiles of the detected rotational lines in the high energy vibrational states show a decreasing linewidth with increasing energy levels. This may evidence that these lines could be excited only in the inner shells, i.e. the densest and hottest, of the circumstellar envelope of IRC+10216.

arXiv comment20 pages, 3 figures. Published in ApJL

References in corpus (10)

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• The Abundance of SiC2 in Carbon Star Envelopes: Evidence that SiC2 is a gas-phase precursor of SiC dust
• Discovery of the first Ca-bearing molecule in space: CaNC
• ExoMol line lists XXV: A hot line list for silicon sulphide, SiS
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• A spectral line survey of IRC +10216 between 13.3 and 18.5 GHz
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• Monitor variability of millimeter lines in IRC +10216
• SiS in the circumstellar envelope of IRC +10126: maser and quasi-thermal emission
• The maser emitting structure and time variability of the SiS lines J=14-13 and 15-14 in IRC+10216
• Clues to NaCN formation
• Chemistry in AGB stars: successes and challenges
• Multi-frequency high spectral resolution observations of HCN toward the circumstellar envelope of Y CVn
• Charting Circumstellar Chemistry of Carbon-rich AGB Stars: I. ALMA 3 mm spectral surveys
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• New SiS destruction and formation routes via neutral-neutral reactions and their fundamental role in interstellar clouds at low and high metallicity values
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• IRC+10216 mass loss properties through the study of $\lambda$3mm emission: Large spatial scale distribution of SiO, SiS, and CS
• The Abundance of SiC${}_2$ in Carbon Star Envelopes
• Laboratory Rotational Spectra of Silyl Isocyanide
• Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars. II. Abundances and spatial distributions of CS