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.

20 pages, 3 figures. Published in ApJL

References in corpus (3)

• Molecular shells in IRC+10216: tracing the mass loss history
• The distribution of SiO in the circumstellar envelope around IRC+10216
• The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations

Cited by in corpus (9)

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• Discovery of SiCSi in IRC+10216: A missing link between gas and dust carriers of SiC bonds
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• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
• A spectral line survey of IRC +10216 between 13.3 and 18.5 GHz
• SiS formation in the interstellar medium through Si+SH gas phase reactions
• Monitor variability of millimeter lines in IRC +10216
• SiS in the circumstellar envelope of IRC +10126: maser and quasi-thermal emission
• Clues to NaCN formation