Imaging a Mosaicked Spectral Line Dataset

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As before, these notes assume that you have made the following global definitions in CASA:

# In CASA
msdir='./'
project='c0xxx'
msfile=msdir+project+'.ms'

If your data are already edited and calibrated, there's really only one step left: clean. Unlike in MIRIAD, which has separate tasks for inverting and cleaning an image, CASA does it in one step. If you want a dirty image, just set niter=0 so that clean doesn't actually do any...cleaning.

Here's a command-line call to clean, which demonstrates many of the interesting parameters you can tweak. This is a simple example, assuming you are making an image of a single field, and you want to clean the whole thing.

Some things of note:

• phasecenter doesn't need to be specified, if you are happy with the phase center that clean derives from the combined mosaicked fields.
• it is important for both imagermode and ftmachine to be set to 'mosaic' if you want your mosaicked data to be stitched together correctly.
• always include units when specifying the threshold at which to stop cleaning.

# In CASA
clean(vis=msfile,imagename='clean_pb',spw='1,2',field='3~51',
      phasecenter='J2000 20h35m35.32 60d10m01.00',
      cell=2.,imsize=[400,400],
      mode='velocity',start='-103.00km/s',width='5.08km/s',nchan=29,
      interpolation='linear',psfmode='clark',
      imagermode='mosaic',ftmachine='mosaic',
      scaletype='SAULT',restfreq='115.2712GHz',interactive=F,
      minpb=0.1,pbcor=True,
      niter=1000,threshold='340mJy',mosweight=False,
      weighting='natural')

To take a look at the image you produced, use the CASA viewer:

# In CASA
viewer(image='clean_pb.image')

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