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Astron. Astrophys. 360, 161-170 (2000)

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Towards global phase-delay VLBI astrometry: observations of QSO 1150+812 and BL 1803+784

M.A. Pérez-Torres 1, J.M. Marcaide 1, J.C. Guirado 1,2, E. Ros 3, I.I. Shapiro 4, M.I. Ratner 4 and E. Sardón 5

1 Departamento de Astronomía y Astrofísica, Universidad de Valencia, 46100 Burjassot, Valencia, Spain
2 Centro de Astrobiología, INTA/CSIC, 26650 Torrejón de Ardoz, Madrid, Spain
3 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
4 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
5 GMV, Isaac Newton 11, 28760 Tres Cantos, Madrid, Spain

Received 21 March 2000 / Accepted 25 May 2000


On 18 November 1993, we observed the QSO 1150+812 and the BL Lac object 1803+784, nearly 15o apart on the sky, with a VLBI array, simultaneously recording at 8.4 and 2.3 GHz. Using difference astrometry techniques, we determined the coordinates of 1803+784 relative to those of 1150+812 to be


These standard errors contain estimated contributions from the propagation medium, the effects of source opacity, and the possible misidentification of the reference point in some of the maps. We obtained comparably accurate and consistent relative positions of the radio sources with GPS-based ionosphere corrections, thus demonstrating that dual-frequency observations are not required for state-of-the-art accuracy in VLBI astrometry. These results also demonstrate the feasibility of using single-frequency measurements for sources separated by 15o on the sky, and open the avenue for the application of this technique on a full-sky scale.

Key words: astrometry – techniques: interferometric – galaxies: quasars: individual: QSO 1150+812 – galaxies: BL Lacertae objects: individual: BL 1803+784

Present address: Istituto di Radioastronomia, Via P. Gobetti 101, I-40129 Bologna, Italy

Send offprint requests to: M.A. Pérez-Torres

Correspondence to: torres@ira.bo.cnr.it

© European Southern Observatory (ESO) 2000

Online publication: July 27, 2000