Continuum Subtraction on an Image Cube (imcontsub)

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6.3 Continuum Subtraction on an Image Cube (imcontsub)

One method to separate line and continuum emission in an image cube is to specify a number of line-free channels in that cube, make a linear fit to the visibilities in those channels, and subtract the fit from the whole cube. Note that the task uvcontsub serves a similar purpose; see § 4.7.5 for a synopsis of the pros and cons of either method.

The imcontsub task will subtract a polynomial baseline fit to the specified channels from an image cube.

The default inputs are:

#  imcontsub :: Continuum subtraction on images
imagename  =      ’’   #  Name of the input image
linefile   =      ’’   #  Output line image file name
contfile   =      ’’   #  Output continuum image file name
fitorder   =       0   #  Polynomial order for the continuum estimation
region     =      ’’   #  Image region or name to process see viewer
box        =      ’’   #  Select one or more box regions
chans      =      ’’   #  Select the channel(spectral) range
stokes     =      ’’   #  Stokes params to image (I,IV,IQU,IQUV)
async      =   False

Area selection using box and region is detailed in § 6.1.1 and § 6.1.5 respectively.

Image cube plane selection using chans and stokes are described in § 6.1.2.

ALERT: imcontsub has issues when the image does not contain a spectral or stokes axis. Errors are generated when run on an image missing one or both of these axes. You will need to use the Toolkit (e.g. the ia.adddegaxes method) to add degenerate missing axes to the image.

6.3.1 Examples for imcontsub)

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