12.1.1 uv table contents

A uv table is a file in the Gildas Data Format, of dimensions [3 +7, ], for spectral channels and visibilities. The $3\ensuremath{N_\mathrm{\scriptscriptstyle C}} +7$ lines contain:

1.

u in meters

2.

v in meters

3.

Scan number

4.

Observation date (integer CLASSday number)

5.

Time in seconds since above date

6.

Number of start antenna of baseline

7.

Number of end antenna of baseline

8.

First frequency point (real part)

9.

First frequency point (imaginary part)

10.

First frequency point (weight)

11.

Same for second frequency point, and so on

Thus for a given scan with antennas, $\ensuremath{N_\mathrm{\scriptscriptstyle A}} (\ensuremath{N_\mathrm{\scriptscriptstyle A}} -1)/2$ visibilities are recorded.

The table header has the standard form of a GILDASImage. The header is available (for instance) by declaring:

 GRAPHIC> SIC\DEFINE HEADER T co10.uvt READ
 GRAPHIC> EXAMINE T%

For a table named co10.uvt. Some keywords convey a more precise meaning for uv tables:

T%NDIM should be 2

T%DIM contains 3 +7 and

T%RA,T%DEC coordinates (radians) of the pointing center (the center of the primary beam).

T%A0,T%D0 coordinates (radians) of the phase tracking center (a point source at this point should have zero phase); they are identical to RA and DEC when a table is first produced.

T%EPOCH The epoch of those coordinates. Should be 2000.0

T%VELOFF, T%VELRES The velocity of the reference channel, and the channel separation in velocity units (km/s)

T%RESTFRE, T%FREQRES The rest frequency, and the channel separation in frequency units (MHz)

T%CONVERT[1,1] the reference channel

T%CONVERT[1,2] the actual observing frequency at the reference channel (MHz); the one used to scale angular displacements from u,v coordinates in meters.

One may also examine directly the header by typing simply :

 GRAPHIC> HEADER co10.uvt