Tentative detection of phosphine in IRC +10216

International audienceAims: The JK = 10-00 rotational transition of phosphine (PH3) at 267 GHz has been tentatively identified with a T_MB ~ 40 mK spectral line observed with the IRAM 30-m telescope in the C-star envelope IRC +10216. Methods: A radiative transfer model was used to fit the observed line profile. Results: The derived PH3 abundance relative to H2 is 6 × 10-9, although it may have a large uncertainty due to the lack of knowledge about the spatial distribution of this species. If our identification is correct, it implies that PH3 has a similar abundance to what is reported for HCP in this source and that these two molecules (HCP and PH3) together take up about 5% of phosphorus in IRC +10216. The abundance of PH3, like that of other hydrides in this source, is not well explained by conventional gas-phase LTE and non-LTE chemical models, and may imply formation on grain surfaces