New molecules in IRC+10216: confirmation of C${}_5$S and tentative identification of MgCCH, NCCP, and SiH${}_3$CN

Abstract

The C-star envelope IRC+10216 harbors a rich variety of molecules, with more than 80 detected to date. During the course of a $\lambda$ 3 mm survey of IRC+10216 carried out with the IRAM 30-m telescope we have detected various weak lines, with antenna temperatures of a few mK, that we assign to rotational transitions of four new molecules. The observation of three lines of C${}_5$S confirms a previous tentative identification of this molecule by Bell et al. (1993) based on a line at 24.0 GHz. We also report the tentative identification of three molecules not yet observed in space: MgCCH, the first metal acetylide detected in space, and NCCP and SiH${}_3$CN, the phosphorus and silicon analogs of cyanogen (NCCN) and methyl cyanide (CH${}_3$CN). We derive the following column densities: $N$(C${}_5$S) = (2-14) $\times$ 10${}^{12}$ cm${}^{-2}$ (depending on the rotational temperature adopted), $N$(MgCCH) = 2 $\times$ 10${}^{12}$ cm${}^{-2}$, $N$(NCCP) = 7 $\times$ 10${}^{11}$ cm${}^{-2}$, and $N$(SiH${}_3$CN) = 10${}^{12}$ cm${}^{-2}$. The S-bearing carbon chain C${}_5$S is less abundant than C${}_3$S, while MgCCH has an abundance in between that of MgNC and those of MgCN and HMgNC. On the other hand, NCCP and SiH${}_3$CN are the least abundant P- and Si-bearing molecules observed to date in IRC+10216. Based on the behavior of similar molecules it is likely that these four species are formed in the outer circumstellar layers of IRC+10216. We discuss possible gas-phase formation routes.

Accepted for publication in A&A

References in corpus (3)

• Detection of circumstellar CH2CHCN, CH2CN, CH3CCH and H2CS
• Confirmation of circumstellar phosphine
• Tentative detection of phosphine in IRC+10216

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