A new dimmconfig that uses PCA

The $STARLINK_DIR/share/smurf directory includes several “dimmconfig” files that package up commonly used groups of configuration parameter values for use by the makemap command.  A new file called dimmconfig_pca.lis has recently been added, which can be combined with  other dimmconfig files to tell makemap to include a PCA model in its iterative algorithm (the PCA model removes noise signals that are correlated between multiple bolometer time-streams). For instance, to use a PCA model when creating a map of a bright extended source, you could run makemap as follows:

% more conf
^$STARLINK_DIR/share/smurf/dimmconfig_bright_extended.lis
^$STARLINK_DIR/share/smurf/dimmconfig_pca.lis
% makemap config=^conf

To process compact sources, change “bright_extended” above to “bright_compact“.

Using a PCA model can help to reduce the spurious extended structures that often appear in SCUBA-2 maps (although this benefit is bought at the cost of a much extended run time). For instance, below are four 850 um maps of DR 21 – the top row shows the maps made with the basic “bright extended” dimmconfig, and the bottom shows eh results of adding in the new PCA dimmconfig:

Below are the mosaics of the four observations, with the difference map shown in between:

As another example, the following panes show similar maps for three observations of the Serpens South field:

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