A&A 539, A79 (2012) Astronomy DOI: 10.1051/0004-6361/201118211 & c ESO 2012 Astrophysics Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex I. Membership of the Cygnus X region K. L. J. Rygl1,2, A. Brunthaler2,3, A. Sanna2,K.M.Menten2,M.J.Reid4,H.J.vanLangevelde5,6, M. Honma7, K. J. E. Torstensson6,5, and K. Fujisawa8 1 Istituto di Fisica dello Spazio Interplanetario (INAF–IFSI), via del fosso del cavaliere 100, 00133 Roma, Italy e-mail:
[email protected] 2 Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [brunthal;asanna;kmenten]@mpifr-bonn.mpg.de 3 National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro 87801, USA 4 Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail:
[email protected] 5 Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands e-mail:
[email protected] 6 Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands e-mail:
[email protected] 7 Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan e-mail:
[email protected] 8 Faculty of Science, Yamaguchi University, 1677-1 Yoshida, 753-8512 Yamaguchi, Japan e-mail:
[email protected] Received 5 October 2011 / Accepted 30 November 2011 ABSTRACT Context. Whether the Cygnus X complex consists of one physically connected region of star formation or of multiple independent regions projected close together on the sky has been debated for decades.