Combining POL2 observations with different reference positions

A bug has recently been fixed in the SMURF pol2map command  that could cause the maps created by pol2map to be blurred or show bad negative bowling around bright sources if the input observations do not all use the same reference point. So if you are using pol2map to combine data from POL2 observations with different reference positions, then you should ensure that you are using a version of starlink that includes the bug fix – i.e. was created on or after 10th January 2019. To check this, do:

% more $STARLINK_DIR/manifests/starlink.version

This will show details about your starlink build, including the date. To update it using rsync from Hilo, see these instructions.

The bug caused the pointing corrections determined at “step 1” to be in error by an amount roughly equal to the change in reference position between observations. These bad pointing corrections in turn lead to various problems (bad bowling or blurring) in the maps created at “step 2”. Consequently, it is not possible to correct an existing bad reduction – the only option is to do the whole reduction again from the start (having first ensured that your starlink installation is up to date).

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