A&A 467, L37-L40 (2007)
Astronomical detection of C , the second interstellar anionJ. Cernicharo1, M. Guélin2, M. Agúndez1, K. Kawaguchi3, M. McCarthy4, and P. Thaddeus4
1 Dpt. Molecular and Infrared Astrophysics, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006, Spain
2 IRAM, Domaine Universitaire, 300 rue de la piscine, 38400 St Martin d'Hères, France
3 Department of Chemistry, Faculty of Science, Okayama University, Tsushimanaka, Okayama 700-8530, Japan
4 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
(Received 6 March 2007 / 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