[1] CSIC, Inst Astrofis Andalucia, Granada, Spain
[2] Inst Astrofis Canarias, Tenerife, Spain
[3] Univ Copenhagen, Astron Observ, Copenhagen, Denmark
[4] Nord Opt Telescope, Tenerife, Spain
[5] INTA, Lab Astrofis Espacial & Fis Fundamental, Madrid, Spain
[6] Univ Bologna, Dipartimento Astron, Bologna, Italy
[7] Univ Ferrara, Dipartimento Fis, I-44100 Ferrara, Italy
[8] CNR, Ist Tecnol & Studio Radiaz Extraterr, Bologna, Italy
[9] Inst Astrophys, Potsdam, Germany
[10] Astron Inst, CZ-25165 Ondrejov, Czech Republic
[11] Uttar Pradesh State Observ, Naini Tal 263129, India
[12] Univ Iceland, Inst Sci, IS-107 Reykjavik, Iceland
[13] Univ Liege, Inst Astrophys & Geophys, B-4000 Liege, Belgium
[14] Osserv Astron V Cerulli, Teramo, Italy
[15] Calar Alto Observ, Almeria, Spain
[16] Kitt Peak Natl Observ, Tucson, AZ 85726 USA
[17] Univ Bonn, Astron Observ, D-5300 Bonn, Germany
[18] Radio Astron Inst, D-53121 Bonn, Germany
[19] Max Planck Inst Astron, D-69117 Heidelberg, Germany
[20] Chinese Acad Sci, Beijing Astron Observ, Beijing 100080, Peoples R China
[21] Nikolaev Univ Observ, UA-327030 Nikolayev, Ukraine
[22] Nikolaev Astron Observ, Nikolaev Space Res Grp, UA-327030 Nikolayev, Ukraine
[23] Space Res Org Netherlands, Utrecht, Netherlands
[24] CNR, Ist Astrofis Spaziale, I-00044 Frascati, Italy