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A uv table is a file in the Gildas Data Format, of dimensions
[3
+7,
], for
spectral channels and
visibilities. The
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,
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
![\ensuremath{N_\mathrm{\scriptscriptstyle V}}](img938.gif)
- 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
Next: 12.1.2 How to create
Up: 12.1 uv tables
Previous: 12.1 uv tables
S.Guilloteau
2000-01-19