Search for anions in molecular sources: C4H- detection in L1527 M. Agúndez, J. Cernicharo, M. Guélin, M. Gerin, M. C. McCarthy and P. Thaddeus A&A, 478 1 (2008) L19-L22 Published online: 12 December 2007 DOI: 10.1051/0004-6361:20078985