WSRT fact sheet

The layout of the WSRT on its East-West baseline. FIGURE .]
The WSRT array consists of 10 fixed and 2 pairs of movable telescopes, placed on a straight East-West line of about 3km length. Each telescope has a diameter of 25m, and a mesh-width of 8 mm. The interval between the 10 fixed telescopes (labeled 0 through 9) is 144m. The movable pair AB is placed on a 300m railtrack immediately to the East of the fixed array; the second movable pair, CD sits on 150m of rail track 1.2 km away.
The positions of the fixed telescopes (0-9) are defined from West to East as 0(144)1296m. The 4 movable telescopes (A,B and C,D) can be moved to increase the uv-coverage. In the standard configurations, all four are moved together, so that their relative positions remains constant: AB=CD=72m, AC=BD=09=1296m, 0A=9C, 0B=9D. Thus, in the Standard Configuration, the only parameter needed to specify the array is the distance 9A:

- 9A=36m: telescopes ABCD are placed at 1332, 1404, 2628, 2700 m
- 9A=54m: telescopes ABCD are placed at 1350, 1422, 2646, 2718 m
- 9A=72m: telescopes ABCD are placed at 1368, 1440, 2664, 2736 m
- 9A=90m: telescopes ABCD are placed at 1386, 1458, 2682, 2754 m

Regular covering of the uv-plane gives the lowest grating sidelobes. This is achieved by placing the movable telescopes in such a way that the 12-hour concentric elliptic uv-tracks are regularly spaced, in the following way:

- 112 hrs: 9A=72m, giving 72m intervals between uv-tracks.
- 212 hrs: add 9A=36m, giving 36m intervals.
- 412 hrs: add 9A=54 and =90m, giving 18m intervals (with the shortest 18m spacing missing).

Smaller intervals between uv-tracks are better, since this causes the first grating ring to have a larger radius. For intervals of 18m (smaller than the telescope diameter), the grating rings will be essentially outside the primary beam.

The redundant spacings in the regular WSRT array can be used for model-independent internal calibration. The visibilities measured by two redundant interferometers (i.e. with the same baseline length and orientation) must obviously be identical. Thus, any differences between them must be caused by instrumental errors, including the effects of the Earth troposhere and ionosphere.

Maximum redundancy occurs if 9A=72m in the standard configuration figure: baselines 9A=AB=CD=72m, and 09=1B=AC=BD=1296m. In this case, there is a `full redundancy solution' for both phase and gain, linking the errors of all 14 telescopes. For other values of the distance 9A, there will still be a full solution for the telescope gain errors, but the phase solution will usually be split up into three independent groups: the fixed array (0-9), A/C and B/D.

Sensitivity

The following tables gives WSRT interferometer system temperatures and sensitivities. The theoretical rms continuum sensitivity for 12 hrs observation is based on the given and maximum bandwidth.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.