TWHydraBand7 Imaging for CASA 3.3

Prepare Continuum Data

In order to speed up imaging for the continuum data we will average channels together, and then flag the few spectral features. This method works well in the case of only a few spectral lines, and will speed the imaging and self-calibration process, while retaining enough channelization to aid in multi-frequency synthesis and seeing spectral features. The amount of channel averaging should be adjusted to your particular data. If necessary one can also flag the spectral features first but in that case make a backup of the analogous file to TWHydra_corrected.ms as you will need it later (unflagged) for spectral line imaging.

# In CASA

# In CASA
split(vis='TWHydra_corrected.ms',outputvis='TWHydra_cont.ms',
       spw='0~3:22~3820',width=100,datacolumn='data')

Now make a plot of amplitude vs. channel to see what needs to be flagged

# In CASA
plotms(vis='TWHydra_cont.ms',spw='0~3',xaxis='channel',yaxis='amp',
      avgtime='1e8',avgscan=T,coloraxis='spw',iteraxis='spw',xselfscale=T)

The CO(3-2) and HCO+(4-3) lines are obvious. The 4th spw; spw=3 also shows an upswing on the highest channels that is problematic, could be a weak atmospheric feature.

# In CASA
flagdata(vis='TWHydra_cont.ms',
         spw=['0:16~16','2:21~21','3:33~37'])

Have a look at the continuum as a function of uv-distance. If the data are flat as a function of uv-distance the source is completely unresolved. If you see structure (in this case decreasing amplitude with uv-distance) the source is resolved.

# In CASA
plotms(vis='TWHydra_cont.ms',spw='',xaxis='uvdist',yaxis='amp',field='',avgchannel='38',
       coloraxis='spw',iteraxis='spw')