Letter to the Editor
Tentative detection of phosphine in IRC +10216*
Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain e-mail: [marce;cerni;pardo]@damir.iem.csic.es
2 Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d'Hères, and LERMA/École Normale Supérieure, 24 rue Lhomond, 75231 Paris, France e-mail: firstname.lastname@example.org
3 California Institute of Technology, Downs Laboratory of Physics 320-47, Pasadena, CA 91125, USA e-mail: email@example.com
Accepted: 27 May 2008
Aims. The JK = 10-00 rotational transition of phosphine (PH3) at 267 GHz has been tentatively identified with a ~ 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.
Key words: stars: individual: IRC +10216 / stars: carbon / radio lines: stars / astrochemistry / line: identification / stars: AGB and post-AGB
Based on observations carried out with the IRAM 30-m telescope and the Caltech Submillimeter Observatory (CSO). IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). The CSO is operated by the California Institute of Technology under funding from the National Science Foundation, Grant No. AST-0540882.
© ESO, 2008