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

TL;DR

This study uses ALMA observations to analyze Si-bearing molecules in the circumstellar envelope of IRC+10216, revealing their spatial distribution, excitation conditions, and potential excitation regions within the envelope.

Contribution

First detection of high-vibrational SiS lines and detailed analysis of SiO and SiC$_2$ distributions in IRC+10216's envelope using ALMA data.

Findings

SiS shows compact emission, SiO and SiC$_2$ are more extended

High-energy vibrational lines have decreasing linewidths

Models suggest SiS lines may be optically thick

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.