Sample Selection

All the calibrators are selected from the VLA calibrator Manual released in 2003. The name used for the sources are the $J2000$ coordinate names.

We chose all the sources which met the following criteria :

• Calibrator quality P ($<$3 % amplitude closure errors expected) & S ($\approx 3-10$ % closure error expected) at all A, B, C & D array configurations of the VLA with no $uv$-limits.
• The source should have a flux density $\ge$0.5 Jy at L band (1420 MHz).
• The sources observable by GMRT i.e. above declination $-53^o$.

The above criteria gave us a list of 150 sources. Most of the sources did not have any $uv$ limits (or $uv$-range, is the range of uv distance from the origin in kilo-wavelengths beyond which the source can't be used as calibrator), only a few sources, namely, $\approx 4$ sources have $uv$ max limit ranging from 60 kL to 100 kL and $\approx 17$ sources have $uv$ min limit ranging from 0.5 kL to 20 kL. All these sources which met the above criteria were observed using GMRT.

The figure 3.1 shows the distribution of the sources observed using GMRT, projected over the sky, for this project.

Figure 3.1: Distribution of Observed Sources on the Sky Plane.