[1] Laboratoire Gemini, UMR 6203, Observatoire de la Côte d'Azur/CNRS, BP 4229, 06304 Nice Cedex 4, France
[2] Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
[3] Laboratoire Universitaire d'Astrophysique de Nice, UMR 6525, Université de Nice - Sophia Antipolis/CNRS, Parc Valrose, 06108 Nice Cedex 2, France
[4] Laboratoire d'Astrophysique de Grenoble, UMR 5571, Université Joseph Fourier/CNRS, BP 53, 38041 Grenoble Cedex 9, France
[5] European Southern Observatory, Casilla 19001, Santiago 19, Chile
[6] Departamento de Astronomia, Universidad de Chile, Chile
[7] Astrophysics Research Institute, Liverpool John Moores University, Birkenhead, CH41 1LD, United Kingdom
[8] Jodrell Bank Observatory, School of Physics and Astronomy, Univ. of Manchester, Macclesfield, SK11 9DL, United Kingdom
[9] CESR, 31028 Toulouse, France
[10] Univ. P. Sabatier, 31062 Toulouse, France
[11] INAF - Osservatorio Astrofisico di Arcetri, Istituto Nazionale di Astrofisica, Largo E. Fermi 5, 50125 Firenze, Italy