Continuum imaging

To avoid this, it is better to deconvolve the continuum emission by averaging as many channels as possible. Line emission should be filtered as much as possible at this level, since otherwise it contaminates the information which is sought. A further issue is that the effective resolution of the array goes as \(\lambda/B\) . With a wide enough frequency coverage, this is a significant change over the bandwidth that must be accounted for. It actually helps to obtain a better uv coverage, a process called bandwidth synthesis.

In IMAGER, the whole process can be done in four commands
uv_preview
uv_filter
uv_map /cont
clean (and optionally uv_restore)

• Command UV_FILTER, used after UV_PREVIEW, will remove all regions of the spectrum that are contaminated (above the noise level) by spectral lines.
• Command UV_MAP /CONT will then image in bandwidth synthesis the remaining continuum emission. After that, CLEAN and UV_RESTORE can deconvolve and properly restore the image.

In command UV_MAP /CONT, the user can specify the spectral index of the emission to optimize the signal to noise by giving the best weight to each spectral channel.

This part is only a first step in a proper analysis. The next one is to image the remaining signal in spectral lines, and ultimately add back the deconvolved continuum image. To help the user in this, the image obtained as above is automatically saved as the CONTINUUM SIC image variable.