EVN u,v coverage
The quality of a VLBI image is usually determined by the density and distribution of UV tracks in the UV plane. These tracks are formed by the 2-D projection of the various interferometer baselines on a plane (the so-called "uv-plane") which is perpendicular to the source direction.
UV coverage of the EVN at 18cm for various source declinations:
- Dec +60 degrees
- Dec +60 degrees (but without Shanghai & Urumqi)
- Dec +20 degrees
As can be seen from these plots, the UV coverage of the EVN at the main observing frequencies (18, 6, 3.6 and 1.3) is excellent for sources above +20 deg declination. Note that the inclusion of the Chinese telescopes (Sh and Ur) extends the UV coverage considerably.
The superb UV coverage obtained with a global VLBI array (EVN+VLBA), is ideal for producing high dynamic range, milliarcsecond resolution images of complex radio sources. "Snap-shot" observations of many sources can also take advantage of the dense UV coverage:
At lower source declinations (< +15 degrees) the coverage of the EVN array becomes foreshortened, resulting in an increasingly elongated beam and poorer uv-coverage. The Hartebeesthoek telescope in South Africa is especially useful for equatorial and southern targets. UV coverage can also be improved by including VLBA telescopes, which generally lie at more southern latitudes compared to the EVN telescopes.
EVN webmaster (jive{at}jive.eu)