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Astron. Astrophys. 336, 385-392 (1998)

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Submilliarcsecond shift of the brightness peak of the radio sources 1928+738 and 2007+777

J.C. Guirado 1, J.M. Marcaide 1, E. Ros 1, M.I. Ratner 2, I.I. Shapiro 2, A. Quirrenbach 3 and A. Witzel 4

1 Departamento de Astronomía, Universitat de València, E-46100 Burjassot, Valencia, Spain
2 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
3 Max Planck Institut für Extraterrestrische Physik, Postfach 1603, D-85740 Garching bei München, Germany
4 Max Planck Institut für Radioastronomie, Postfach 2024, D-53010 Bonn, Germany

Received 6 January 1998 / Accepted 21 April 1998


From two sets of very-long-baseline interferometry (VLBI) observations, one each at 5 GHz (1985.77) and at 2.3 and 8.4 GHz simultaneously (1988.83), of the quasar 1928+738 phase-referenced to the BL Lac object 2007+777, we infer a change in their relative position of 0.74[FORMULA]0.22 milliarcseconds (mas) along a position angle of [FORMULA], where the quoted standard errors account for errors in our models of the geometry of the interferometric array, the atmosphere, and the source structure. This change is interpreted as an (inadvertent) shift of the reference point selected in the structure of 1928+738, due to the presence of an emerging component; different opacity effects in the three observing frequency bands may also be a significant contributor.

Key words: astrometry – techniques: interferometric – quasars: individual: 1928+738 – quasars: individual: 2007+777

Send offprint requests to: J.C. Guirado

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© European Southern Observatory (ESO) 1998

Online publication: July 7, 1998