XYPHS_
xx, where xx is your AIPS number)
containing the XY phase for each antenna into the FITS area (/DATA/FITS). Text files of system temperature are also written.
Although the various selection parameters of ATLOD
are still active,
you probably want to see all the data. Most of the other ATLOD
parameters are unimportant for this.
AIPS/ATLOD | |
optype = 'sysc' | Load the data |
freqsel | Select all data |
ifsel | |
source | |
timer |
You should plot the phases (and the system temperatures) with the Unix program pltsys - which prompts you for the name of the text file to plot as well as other information. Examine these plots carefully to assess their quality. You should use these plots to choose your reference antenna (for calibration purposes). Choose the reference antenna to be the antenna having the cleanest, most stable XY phase measurements.
Determine some mean value of the XY phase for each antenna from the plots. The command pltsys prints out both the average and median XY phase. As there are often outliers, the median is more likely to reflect the true XY phase value. Getting a good value is only important for the reference antenna. Do not be too concerned if there are large jumps in the XY phases on antennas other than the reference antenna.
XYPHS_
xx.
If you are going to correct the XY phases in Miriad, or if you are not going to correct XY phase at all, then you should now load your data without applying any XY phase. It is probably worth your while to pretend that the polarisations are circular rather than linear with the usual fudges, as not all the AIPS software will recognise linears (most of the calibration software will). You must not convert to Stokes parameters. The appropriate ATLOD parameters are
AIPS/ATLOD | |
optype = 'load' | Load the data |
aparm(1) =-1 | Label as circular |
cparm(5) =0 | Do not apply any XY phases. |
AIPS/ATLOD | |
optype = 'load' | Load the data |
aparm(1) =-1 | Label as circular |
cparm(4) =1 | Use xyphase array and |
not the on-line values | |
cparm(5) =1 | Apply XY phase to Y gains |
xyphase | Assign the XY phases here |
For continuum work, to save disk space and to speed access to the data, you may consider averaging your channels together to form ``channel-0'' datasets, using task AVSPC. While this causes very little degradation for 3 cm observations, forming ``channel-0'' results in bandwidth smearing in 13 and 20 cm observations, and so is probably inadvisable for high dynamic range work there. For high dynamic range work at 6 cm, it is debatable whether averaging is detrimental. If in doubt, do not average. It is always possible to form a channel-0 dataset later anyway.
One other consideration in determining whether or not to average is whether
or not you are going to apply XY phase corrections with task atxy.
For obscure reasons, if you used AIPS ATLOD,
atxy
needs to know the ``sideband indicator''
of the data. The sideband indicator, which is , is copiously
reported by ATLOD, both in its output to the terminal, and in the
history file. The sideband indicator also happens to be the sign of the
channel frequency increment. This is how atxy
normally determines
them.
However, if you form a channel-0 dataset, the sign
of the frequency increment is lost! So if you give atxy
a channel-0
dataset, you will also have to tell it the sideband indicators.
You must give it a sideband indicator for each IF. Provided the
sideband indicator remains constant with time, this is little more than
an annoyance. However if the sideband indicator varies with time, you
are in some trouble. Overall it is best not to form
channel-0 datasets if you used AIPS ATLOD and you are going to
use atxy.
After flagging (and possibly averaging), write your data as a FITS file using FITTP. It is probably most convenient to write out a multi-source file. At this stage you have no calibration - only flagging tables (which you can apply in Miriad later).
FITS | |
in=MULTI.FITS | FITS multi-source file to be loaded into Miriad |
op=uvin | Read uv data in |
out=multi.uv | The output Miriad dataset. |
FGFLAG | |
vis=multi.uv | Apply AIPS flagging table to the data. |
At this stage it is worth running uvindex. This produces a summary of your dataset, which you should probably save in a log file. Inspect this summary carefully, particularly the frequencies (especially in fits complained about inconsistent frequency definitions). If the frequency information looks incorrect, read Chapter 8 more carefully and/or seek help.
UVINDEX | |
vis=multi.uv | Dataset to summarise. |
log=multi.log | Output log file. |
XYPHS_
xx,
where xx is your AIPS user number.
Task atxy
can also be used to correct the XY phases of
data loaded with Miriad atlod
where options=xycorr
was not used.
In this case, the on-line XY phase measurements are contained
within the dataset (as the variable xyphase
), and you do not require
a input text file.
ATXY | |
vis=multi.uv | The input dataset. |
xyphase=XYPHS_56 | The input AIPS ATLOD XY |
phase text file, or | |
xyphase | leave unset if Miriad atlod was used. |
refant=3 | Correct antenna 3 in time varying way. |
interval=# | Solution interval. Default is 30 min |
sideband | Sideband indicator. Leave unset for |
multi-channel data. | |
out=multi.uvxy | Output XY phase corrected data. |
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