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Astron. Astrophys. 348, 381-393 (1999)

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High precision difference astrometry applied to the triplet of S5 radio sources B1803+784/Q1928+738/B2007+777

E. Ros 1, J.M. Marcaide 1, J.C. Guirado 1, M.I. Ratner 2, I.I. Shapiro 2, T.P. Krichbaum 3, A. Witzel 3 and R.A. Preston 4

1 Departament d'Astronomia i Astrofísica, Universitat de València, E-46100 Burjassot, València, Spain
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
3 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
4 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove, Pasadena, CA 91109, USA

Received 2 September 1998 / Accepted 6 April 1999


We determined the separations of the radio sources in the triangle formed by the BL Lac objects 1803+784 and 2007+777, and the QSO 1928+738 from intercontinental interferometric observations carried out in November 1991 at the frequencies of 2.3 and 8.4 GHz simultaneously. Difference phase-delay astrometry yielded the following separations:


We successfully connected differenced phase delays over 7o on the sky at 8.4 GHz at an epoch of maximum solar activity. The effects of the ionosphere on these VLBI data were mostly removed by estimates of the total electron content from observations of GPS satellites. The comparison of the estimated separation of QSO 1928+738 and BL 2007+777 with previous such estimates obtained from data at different epochs leads us to a particular alignment of the maps of QSO 1928+738 at different epochs relative to those of BL 2007+777, although with significant uncertainty. For this alignment, that the jet components of QSO 1928+738 show a mean proper motion of 0.32[FORMULA]0.10 mas/yr and also suggest an identification for the position of the core of this radio source.

Key words: techniques: interferometric – astrometry – galaxies: BL Lacertae objects: individual: B1803+784; B2007+777; Q1928+738

Present address: Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Send offprint requests to: E. Ros (ros@mpifr-bonn.mpg.de)

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999