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: