-
Towards global astrometry: VLBI observations of QSO 1150+812
and BL 1803+784,
M.A. Pérez-Torres, J.M. Marcaide, J.C. Guirado, E. Ros, I.I.
Shapiro, M.I. Ratner, E. Sardón
Astronomy & Astrophysics, 360:161-170 (2000)
- Abstract
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
Δα = 6h7m33.s18469 +/- 0.s00020
Δδ = -2o30'25."13557 +/- 0."00075
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 15o
on the sky, and open the avenue for the application of this technique
on a full-sky scale.
Eduardo Ros
ros@mpifr-bonn.mpg.de