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A table header contains all the informations of a GDF header but some
of these informations have a special meaning in this context. The
HEADER is the standard way inside GILDAS to display in a human
readable way the header of GDF file. For instance, MAPPING> header
12cs21.uvt would display
1 W-GDF_RHSEC, Absent section NOISE
2 File : 12cs21-1.uvt REAL*4
3 Size Reference Pixel Value Increment
4 154 25.50000000000000 97980.02890200325 -6.5365856842222472E-02
5 1320 0.000000000000000 0.000000000000000 1.000000000000000
6 1 0.000000000000000 0.000000000000000 0.000000000000000
7 1 0.000000000000000 0.000000000000000 0.000000000000000
8 Blanking value and tolerance 1.23455997E+34 0.0000000
9 Source name HORSEHEAD
10 Map unit Jy
11 Axis type UV-RAW RANDOM UNKNOWN UNKNOWN
12 Coordinate system EQUATORIAL
13 Right Ascension 05:40:53.903 Declination -02:28:22.00
14 Lii 206.9592680349889 Bii -16.80061668685155
15 Epoch 2000.0000
16 Projection type AZIMUTHAL Angle 0.000000000000000
17 Axis 0 A0 05:40:54.270 Axis 0 D0 -02:28:00.00
18 Minimum 0.0000000 at 0 0 0 0
19 Maximum 0.0000000 at 0 0 0 0
20 Axis 1 Line Name 12CS(2-1) Rest Frequency 97980.95299999999
21 Resolution in Velocity 0.20000000 in Frequency -6.5365856842222472E-02
22 Offset in Velocity 10.500000 Image Frequency 0.000000000000000
23 Noise
24 Beam 2.494E-04 0.00 0.00
Comments:
- Line 2
- Indicates the filename associated to the currently displayed
header.
- Lines 3-7
- Display the dimensions of the associated array. Here it is
a rank 2 array of dimension 1320 columns times 154 lines, i.e. 1320
visibility spectra of 49 frequency channels (see previous section). Line
4 describes the frequency axis of the visibility spectra stored in the
table. Be careful that this is a convention, i.e. it must be
decoded using the particular form of the table. In our case, each spectra
has 49 frequency channels of width -65.36 kHz, the frequency of the
reference pixel 25.50 corresponding to 97980.02890200325 MHz. This last
frequency is the frequency delivered by the correlator, i.e. seen by the
observatory. In particular, this is the frequency that must be used to
compute the primary beam of the interferometer.
- Line 10
- Indicates the unit of the real and imaginary parts of the
visibilities. *** Weights unit? JP ***
- Line 11
- Indicates that this is table (UV-RAW and
RANDOM).
- Lines 12-15
- Describe the coordinate system.
- Lines 16-17
- Describe the projection system. In the table
format, A0 and D0 indicate the phase center while
Right Ascension and Declination indicate where the
antenna pointed when acquiring the signal. These information are in
general identical for single field imaging and different for mosaicing.
- Lines 18-19
- Unused for tables.
- Lines 20-22
- Describe additional information about the frequency axis
of the visibility spectra. In particular, the rest frequency (here
97980.953 MHz) corresponding to a velocity of 10.5 km/s in the velocity
frame (in general LSR).
- Line 23
- Unused for tables.
- Line 24
- Indicates the primary beam size of the interferometer in
radian (This is an indirect way to pass the size of the interferometer
antennas).
Next: Interacting with table
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Previous: table
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Gildas manager
2024-04-18