IMAGING step
Keywords: imager

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### `IMAGING` step

The `IMAGING` button will scan all spectral windows to identify whether they can be used to produce a Continuum or spectral line image.

Low resolution spectral windows, identified as those whose resolution is coarser than blue`ALL%MINFRES` will be used to produce continuum images, by filtering any detected spectral signature in the data before.

High resolution spectral windows, identified as those whose resolution is better than blue`ALL%MINFRES`, data cubes will be produced.

In `SPLIT` Mode, if a Line Catalog is present, these high spectral resolution windows will be scanned for line identifications. For each spectral line in the current catalog(s) (defined by command magenta`CATALOG`) that fall in a spectral window, a continuum-free UV table will be created, covering the velocity range specified by the user (by variable blue`ALL%RANGE`) around the line frequency. The naming convention is the following:

      original-molecule-I-X

where
- `original` is the name of the initial high resolution spectral window
- `molecule` is the name of the spectral line in the catalog
- `I` is a sequence number, incremented each time a new line is found from the same original UV table.
- `X` is a character code, equal to `D` if the line is suspected to be detected, and to `U` if not. When several lines are too close together, the `D` status may be incorrectly affected, but this is just a naming convention, not a strong result.

In addition an

      original-C

file that contains (presumably) line-free emission only is created for each original UV table.

The imaging results are stored in a specific sub-directory (`./MAPS/` by default, controlled by blue`all%maps`). Only the Clean Component Table (cyan`.cct`) and Clean image (cyan`.lmv-clean`) files are written.

When no Line catalog is present, only 3 images are produced for each UV tables: starting froml the `original` name

      original-C       original-U    and   original-A

The ...`-C` contains (an estimate of) line-free emission, averaged over the bandwidth of the UV data. The ...`-U` is the continuum subtracted image, while in ...`-A` the pseudo-continuum image obtained in ...`-C` has been added back. The ...`-A` thus contains all the signal, and can be used to provide a better estimate of the continuum level using e.g. the magenta`MAP_CONTINUUM` command.

Spectral resampling can be performed by appropriate setting of blue`ALL%RANGE`. If non zero, blue`ALL%RANGE[3]` indicates the desired spectral resolution. Furthermore, in the magenta`CATALOG` case, blue`ALL%RANGE[1:2]`, if non zero, specify the Min and Max velocities imaged around each spectral line.

In `ALL` mode, the behaviour is similar, but only the `-C` and `-A` products are created.

In `CONTINUUM` mode, line emission is assumed to be negligible, and only the `-C` continuum images are produced.

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