Documentation on atxy

Task: atxy
Purpose: Apply on-line XY phase measurements to Miriad data.
Categories: uv analysis

        ATXY corrects data for XY phase errors. It determines the XY phase
        measurements, either from the xyphase visibility variable or from
        the text file written by AIPS ATLOD, averages them, and then
        applies them to the data. The averaging step consists of finding
        the median XY phase in a given interval.

Key: vis
        The names of the input uv data sets. No default.

Key: xyphase
        If the data were loaded with Miriad ATLOD, then they should contain
        the on-line XY phase measurements in the xyphase variable. Howver
        if the data were loaded with AIPS (and then transferred to Miriad
        via FITS files), then you must give the name of the XY phase
        text file written by AIPS. Generally it will be XYPHS_xx, where
        xx is an AIPS user number.

Key: refant
        Antennas to apply XY phase corrections to. Generally it is best to
        apply corrections to only a single antenna -- the antenna which you
        have the greatest confidence in the XY phase measurements. Often
        this antenna will be the reference antenna during the observation.
        If you apply the XY phase to a subset of antennas, one of these
        antennas should be used as the ``refant'' antenna to GPCAL.
        No default.

Key: interval
        This gives the length of an averaging interval, in minutes. The
        default is 30 minutes, but larger values may be useful.

Key: break
       The times, in the normal Miriad format, where there are 
       break points. A ``break point'' gives a time where some form of
       instrumental glitch took place, and the xyphases jumped. By
       giving a break point, you prevent a solution interval from spanning
       this time.

Key: sideband
        Sideband indicators. If the input was loaded with AIPS ATLOD, and
        if you averaged it into a channel-0 data-set, you must give the
        sideband indicator (+1 or -1) for each IF. This information is needed
        to convert between the AIPS and Miriad XY phase convention.
        If the input is still multi-channel data, or you used Miriad ATLOD,
        it is wiser to let this parameter default. Note that ATXY cannot
        cope with channel-0 data-sets when the sideband indicators
        change with time.

Key: out
        The name of the output uv data set. No default.

Key: options
        Extra processing options. Several options can be given,
        separated by commas. Minimum match is supported. Possible values
        are:
          srcbreak  Generate break points every time there is a change
                    in source.
          undo      Apply the negative of the XY phase correction. There
                    should be no sensible reason to ever use this option.
          reweight  Reweight the data (in the lag domain) to minimise the
                    so-called Gibbs phenomena and to help localise
                    interference.