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Basic Information on pmosmem
Task: pmosmem
Purpose: Maximum Entropy deconvolution for polarization mosaics
Categories: deconvolution
PMOSMEM is a MIRIAD task which performs a joint maximum entropy
deconvolution of polarized mosaiced images. Optionally it can
perform a joint deconvolution with a single dish image as well.
Key: map
Two to five input images. The first must be a Stokes-I mosaic,
then one or more polarized mosaics (Stokes Q, U and V images), and then
optionally a c Stokes-I single dish image. These should have
units of Jy/beam. The mosaics should be produced by INVERTs mosaic mode.
All the images must be on exactly the same pixel grid. If necessary,
use REGRID to make this so.
Key: beam
One or perhaps two input dirty beams. The first, corresponding to the
mosaics, will be produced by INVERTs mosaic mode. There
is no default. The second dirty beam (which must be given if there
are two dirty map inputs) gives the point-spread function of the
single dish dirty map. This second dirty beam need not be the same
image size as the input dirty maps, and may be appreciably smaller.
This single-dish beam is assumed to be position-independent, but it
need not be symmetric.
Key: default
The default image. This is the Stokes-I image that the final solution
will tend towards. The final result will be influenced by this default
if the constrains that the data put on the solution are weak.
The default is a flat estimate, with the correct flux.
Key: out
The name of the output map. The units of the output will be Jy/pixel.
It can be input to RESTOR to produce a restored image, or alternatively
to PMOSMEM, as a model, to continue the deconvolution process.
Key: niters
The maximum number of iterations. The default is 30.
Key: region
This specifies the region to be deconvolved. See the Users Manual
for instructions on how to specify this. The default is the entire
image.
Key: tol
Tolerance of solution. There is no need to change this from the
default of 0.01.
Key: q
One or two values (corresponding to the mosaic and single dish
observations). These give estimates of the number of points per beam.
PMOSMEM can usually come up with a good, image-dependent estimate.
Key: rmsfac
PMOSMEM must be able to the theoretical rms noise of the input dirty
map(s), and will, by default, attempt to reduce the residuals to have
the same rms as this. If the true rms noise is different from the
theoretical, you may give the factor to multiply by to convert from
theoretical to true rms noise.
The theoretical rms will usually be an optimistic estimate of the
true noise level. The true noise will be increased by calibration
errors, confusion, poorly understood distant sidelobes, etc.
The rmsfac factor gives some `fudge factor' (usually greater than 1)
to scale the theoretical noise estimate by. Either one or two values
can be given, with the second value corresponding to the single dish
input.
For a mosaic, the theoretical rms is position dependent, and is
determined from information save by INVERT (the mostable table).
For a single dish image, the rms is assumed to be constant across
the field, and given by the "rms" item in the image. If the single
dish input does not contain this item, then this must be added
before using PMOSMEM. This is easily done: for image xxxx, use
puthd in=xxxx/rms value=????
where "????" is the rms noise in Jy/beam.
Key: factor
The flux calibration factor. This is only relevant when doing a
joint deconvolution of a mosaic and a single-dish image. It gives the
factor which the single-dish data should be multiplied by to convert
it to the same flux units as the mosaic. The default is 1.
Key: flux
An estimate of the integrated flux of the source. This parameter cannot
be used if there is an input single dish image.
Giving PMOSMEM a good value for the integrated flux
will help it find a good solution. On the other hand, giving
a poor value may do harm. Normally PMOSMEM will NOT constrain the
integrated flux to be this value, but see the ``doflux'' option below.
The default is image-dependent.
Key: options
Task enrichment parameters. Several can be given, separated by
commas. Minimum match is used. Possible values are:
doflux Constrain the solution to have the correct integrated flux
(normally the integrated flux is not constrained). The
integrated flux is determined from the "flux" parameter or
(if no flux parameter is given) from the default image.
This option cannot be used if a single dish input map is
also given.
dofactor Solve for the flux calibration factor.
verbose Give lots of messages during the iterations. The default
is to give a one line message at each iteration.