Phase Calibration Sources in the Northern Sky at Galactic Latitudes |b| < 25

摘要

The Jodrell Bank–VLA Astrometric Survey (JVAS) of flat-spectrum sources yielded a catalog of 2118 compact radio sources in the northern sky. Those sources are being used as phase calibrators for many synthesis arrays. JVAS suffers from a zone of avoidance because Galactic confusion prevented selection of flat-spectrum sources at |b| < 25. This confusion problem was overcome by selecting variable sources from the GB6 Catalog in the JVAS zone of avoidance. A subset of these sources were observed at 8.5 GHz with the NRAO VLA in the JVAS style, leading to 29 compact radio sources in the zone of avoidance whose positions have been measured to an rms accuracy of about 10 mas or less. This extension of the JVAS lists to lower Galactic latitudes (1) improves the prospects for VLBA phase-referencing of Galactic targets and (2) strengthens the lists' usefulness for studies of the Galactic interstellar medium.