Re-evaluation of ALMA detection of circumstellar \(\hbox {PH}_3\) in the AGB envelope IRC\(+\)10216: Evidence for misidentification with HCN

The article ‘Confirmation of interstellar phosphine towards asymptotic giant branch star IRC\(+\)10216’ by A. Manna and S. Pal uses ALMA data of the C-star envelope IRC\(+\)10216 to claim a confirmation of the detection of \(\hbox {PH}_3\) in this source. The article, however, incorrectly assigns an emission feature observed in the ALMA spectrum of IRC\(+\)10216 to \(\hbox {PH}_3\), while we find that it arises from a highly vibrationally excited state of HCN. Concretely the feature can be confidently assigned to the \(J=3\)–2, \(\ell =0\) transition of HCN in the \(\nu _1 + 4\nu _2\) vibrational state based on the observation of the \(\ell = +2\) and \(\ell = -2\) components of the same rotational transition, \(J=3\)–2, with the observed relative intensities in agreement with the relative line strengths. The detection of \(\hbox {PH}_3\) in IRC\(+\)10216 remains confirmed based on the observation of the \(J=1\)–0 and \(J=2\)–1 lines with the single-dish telescopes IRAM 30m, ARO SMT 10m, and Herschel (Agúndez et al. 2008, 2014; Tenenbaum & Ziurys 2008).