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. This can be improved by including VLBA telescopes at southern latitudes. One interesting possibility is the inclusion of the unaffiliated telescope at Hartebeesthoek (Hh), in South Africa:
EVN webmaster (jive@jive.nl)