Primary Beam Correction for Single Field

The images constructed from calibrated UV data are attenuated by the primary beam. For the SMA dish with 6 m in diameter, the primary beam of the SMA can be described by a Gaussian with a size depending on the observing frequency. Miriad task pbplot calculates and plots the primary beam profile for a given telescope and an observing frequency:

  Task:   pbplot
  telescop = sma            %telescope
  freq     = 219            %observing frequency in GHz
  device   = /xs            %display device 

For a single field observation, the primary beam correction for an SMA image can be done with Miriadtask linmos if the image header parameter Telecope=SMA:

 Task:   linmos
  in       = sgrb2mL.icln          %the input line image cube
  out      = sgrb2ml.icln.pbcor    %the output line image cube
                                   %with correction for primary
                                   %beam 

Before running linmos, one may use prthd to check up the image header. If the header parameter Telescope is not properly specified, one needs to reset the FWHM of the primary beam to the image giving a type of the primary, say, Gaussian for SMA before running linmos:

  Task:   puthd
  in       = sgrb2mL.icln/pbtype
  value    = gaus(50.4)

Alternatively, one can combine a few Miriad tasks to carry out the primary beam correction. First, using pbplot, one calculates the primary beam size:

  Task:   pbplot
  telescop = sma             %telescope
  freq     = 219.08899       %observing frequency
  device   = /xs             %display device

The FWHM (0.84 arcmin or 50.4 arcsec) of the primary beam at the frequency is reported on the terminal. Then, using imgen, one can generate a primary beam model:

  Task:   imgen
  in       = sgrb2mL.icln11
  out      = sgrb2ml.pbmodel
  factor   = 0
  object   = gaussian
  spar     = 1,0,0,50.4,50.4,0

This produces a primary beam model image (sgrb2ml.pbmodel). One may display the primary beam model image with cgdisp prior to correcting for primary beam.

Miriad maths can divide the image by the primary beam model image:

  exp      = sgrb2mL.icln11/sgrb2ml.pbmodel   %the math expression for primary 
                                              %beam correction.
  mask     = sgrb2ml.pbmodel.gt.0.5           %cutoff based on model's intensity.
  out      = sgrb2ml.pbcor                    %output image with PB correction.