Letter to the Editor
Search for anions in molecular sources: C4H- detection in L1527*
Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain e-mail: [marce;cerni]@damir.iem.csic.es
2 Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France e-mail: firstname.lastname@example.org
3 LERMA, UMR 8112, CNRS, Observatoire de Paris and École Normale Supérieure, 24 rue l'Homond, 75231 Paris, France e-mail: email@example.com
4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: [mccarthy;pthaddeus]@cfa.harvard.edu
Accepted: 28 November 2007
Aims.We present the results of a search for the negative ion C4H- in various dark clouds, low mass star-forming regions and photon-dominated regions (PDRs). We have also searched for C6H-, C2H- and CN- in some of the sources.
Methods.The millimeter-wave observations were carried out with the IRAM-30 m telescope.
Results.We detect C4H-, through the and rotational transitions, in the low mass star-forming region L1527. We thus confirm the tentative detection of the line recently reported toward this source. The [ C4H-] /[ C4H] ratio found is 0.011%, which is slightly lower than the value observed in IRC +10216, 0.024%, but above the 3σ upper limit we derive in TMC-1, <0.0052%. We have also derived an upper limit for the [ C6H-] /[ C6H] ratio in the Horsehead Nebula, and for various anion-to-neutral ratios in the observed sources. These results are compared with recent chemical models.
Key words: astrochemistry / ISM: molecules / radio lines: ISM
© ESO, 2008