[1] Univ Ghent, Sterrenkundig Observ, B-9000 Ghent, Belgium
[2] Univ Vienna, Inst Astron, A-1180 Vienna, Austria
[3] Univ Durham, Dept Phys, Durham DH1 3LE, England
[4] Univ Lyon, F-69000 Lyon, France
[5] Univ Lyon 1, F-69622 Villeurbanne, France
[6] Observ Lyon, Ctr Rech Astron Lyon, F-69561 St Genis Laval, France
[7] CNRS, UMR 5574, Lyon, France
[8] Ecole Normale Super Lyon, F-69364 Lyon, France
[9] Observ Paris, GEPI Observ, F-92195 Meudon, France