A new Starlink release contains notable updates to the SCUBA-2 configuration files.

The latest Starlink release - 2014A - has been made public. For details please read the release notes provided at: http://starlink.jach.hawaii.edu/starlink/2014A

As part of this new release we want to highlight one significant update and a couple of new additions to the SCUBA-2 reduction arsenal of config files.

Updates to bright_extended config file

This config file 'dimmconfig_bright_extended.lis' has always been intended for reducing data containing bright extended sources. It has remained untouched for a couple of years now despite advances in our understanding of SCUBA-2 reduction of bright regions. The config file now contains the following parameters/links:

   ^$STARLINK_DIR/share/smurf/dimmconfig.lis

   numiter=-40
   flt.filt_edge_largescale=480
   ast.zero_snr = 3
   ast.zero_snrlo = 2

   ast.skip = 5
   flt.zero_snr = 5
   flt.zero_snrlo = 3

In previous Starlink releases i.e. Hikianalia, the bright_extended configuration file only contained the following:

   numiter = -40
   ast.zero_snr = 5

   flt.filt_edge_largescale = 600

New 'FIX' config file

Two new config parameter files have been added These are intended to be used with one of the existing dimmconfig files. They provide new values for selected parameters aimed at solving a particular problem ("blobs" in the final map, or very slow convergence).

• dimmconfig_fix_blobs.lis 
• These parameters attempt to prevent smooth bright blobs of emission appearing in the final map. It does this by 1) identifying and flagging samples that appear to suffer from ringing a soft-edged Butterworth filter in place of the normal hard-edged filter, and 3) rejecting samples for which the separate sub-arrays see a markedly different common-mode signal.

• dimmconfig_fix_convergence.lis
• The parameters defined by this file attempt to aid the convergence process, and should be used for maps that will not converge within a reasonable number of iterations.

Spotting chunking caused by insufficient memory

It has been shown that better maps are created if all available time stream data are processed in a single chunk to create a single map. If the available memory is too small to allow this to happen, the data will be split into multiple chunks and a separate map made from each chunk, which are all co-added at the end to make the final map.

Thus it can be important to spot whether or not your map was "chunked" or not. Until recently the only option was to trawl through the makemap screen output looking for the warning about insufficient memory. Now, however, you also have an option to tell makemap to abort immediately with an informative error message if the data would be chunked due to insufficient memory (no output map is created in this case). To do this, add "memcheck=1" to your config.

Note, this only affects what happens if the data is processed in chunks due to lack of memory - if chunking is caused by the time-series data being intrinsically discontiguous then a map is still created even if memcheck is set to 1.

It will be necessary to rsync the stardev system from Hilo to use this feature. See starlink.jach.hawaii.edu/starlink/rsyncStarlink

Calibrating SCUBA-2 data in surface brightness units

In most cases the default calibration for SCUBA-2 data processed by the ORAC-DR pipeline is mJy beam^-1. The exception is the recipe for extended sources, REDUCE_SCAN_EXTENDED_SOURCES, which calibrates data in mJy arcsec^-2.

Unfortunately there was an error in an earlier version of this recipe which meant that the FCF was applied incorrectly. The corrected method is available now with an update of ORAC-DR (either from github or via rsync from JAC). If you have data processed with this recipe (either by running it yourself, or downloading processed products from CADC) then re-calibrating the data is easy: simply divide by the pixel area using KAPPA cdiv.

There is a new PICARD recipe for easy calibration of maps produced by running makemap by hand. CALIBRATE_SCUBA2_DATA allows data to be calibrated in in per-beam and surface brightness units. With no parameters, this recipe will calibrate data in mJy beam^-1. For surface brightness calibration, set the recipe parameter USEFCF to 1 and FCF_CALTYPE to ARCSEC, and the recipe will then use the default ARCSEC FCF for the wavelength of the given data.

The recipe can also convert the calibration from one type to another. If your data are already calibrated in mJy beam^-1, they can be given to CALIBRATE_SCUBA2_DATA with the FCF_CALTYPE recipe parameter above, and the recipe will create a new file (with suffix _cal) with units of mJy arcsec^-2. The value and units of the FCF are written into the FITS header of the calibrated file.

The companion recipe, UNCALIBRATE_SCUBA2_DATA, will undo the current calibration, reverting the units to pW in the output file (which has a suffix of _uncal).

Using ORAC-DR or PICARD to perform the (un)calibration is preferred to simply multiplying your data by the FCF as they also set the units correctly for the output files(s), and write the value of the FCF used into the FITS header of the file.

However, there is one note to highlight: the recommended way to calibrate data (either from raw or when changing from per beam to per square-arcsec) is to calibrate the individual observations first, and then coadd those (re)calibrated files. Calibrating or re-calibrating coadds will fail because the coadding step was recently updated to remove FITS header entries that differ between the input files. These usually include the UTDATE which is used by the ORAC-DR calibration system. A future upgrade will provide a workaround though the recommendation to calibrate individual observations stands.