Astrometric accuracy of phase-referenced observations with the VLBA and EVN

¹ Observatoire de Bordeaux (OASU) - CNRS/UMR 5804, BP 89, 33270 Floirac, France e-mail: pradel@obs.u-bordeaux1.fr
² Observatoire de Paris - CNRS/UMR 8112, 61 avenue de l'Observatoire, 75014 Paris, France

Received: 8 March 2005
Accepted: 4 January 2006

Abstract

Astrometric accuracy of complex modern VLBI arrays cannot be calculated analytically. We study the astrometric accuracy of phase-referenced VLBI observations for the VLBA, EVN and global VLBI array by simulating VLBI data for targets at declinations , , , , and . The systematic error components considered in this study are calibrator position, station coordinate, Earth orientation and troposphere parameter uncertainties. We provide complete tables of the astrometric accuracies of these arrays for a source separation of either along the right ascension axis or along the declination axis. Astrometric accuracy is as at mid declination and is as at low () and high () declinations for the VLBA and EVN. In extending our simulations to source separations of and , we establish the formula for the astrometric accuracy of the VLBA: (μas) where is the astrometric accuracy for a separation provided in our tables for various declinations and conditions of the wet troposphere. We argue that this formula is also valid for the astrometric accuracy of the EVN and global VLBI array.