Letter to the Editor
Astronomical detection of C, the second interstellar anion*
Dpt. Molecular and Infrared Astrophysics, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006, Spain e-mail: firstname.lastname@example.org
2 IRAM, Domaine Universitaire, 300 rue de la piscine, 38400 St Martin d'Hères, France e-mail: email@example.com
3 Department of Chemistry, Faculty of Science, Okayama University, Tsushimanaka, Okayama 700-8530, Japan
4 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
Accepted: 30 March 2007
Aims.Following the recent detection of C6H- in the laboratory and in space we have succeeded in studying the microwave spectrum of C4H-. We report here the first detection in space of this negative ion.
Methods.We have observed in the envelope of the carbon star IRC +10216 five lines corresponding to the J = 9-8, 11-10, 12-11, 14-13 and 15-14 rotational transitions of C4H-. The C4H- lines have a cusped shape, denoting that this ion is formed in the outer part of the envelope, like its neutral counterpart C4H.
Results.The abundance of C4H- in IRC+10216 is 1/6 of the abundance of C6H- and 1/4200 of that of C4H.
Conclusions.The detection of C4H-, after that of C6H-, confirms the theoretical prediction that C-chain anions are abundant in interstellar clouds and yields a first measurement of the electron radiative attachment rates.
Key words: stars: individual: IRC+10216 / stars: carbon / radio lines: stars / astrochemistry / line: identification / stars: AGB and post-AGB
© ESO, 2007