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There were two main goals.
Apercal is the result of the work of Bjorn Adebahr (and before him Brad Frank and Nicholas Vilchez) under the supervision of Tom Oosterloo. It is a Miriad-based pipeline which should produce images and line cubes for the imaging surveys that Apertif will carry out. Thijs van der Hulst, Joris Verstappen and Mike Sipior have been preparing the Happili cluster to run the pipeline.
The commissioning members familiarised themselves with the self-calibration and imaging pipeline by working through the provided tutorials and also by using a WSRT data set of 16 pointings of the Lockman Hole area. The fine tuning of the parameters is still in progress, but the results are very encouraging and good images were obtained.
The figure shows one of the images obtained during the BW, reaching 15 microJy/beam noise and full resolution of about 10 arcseconds. The whole cycle (selfcal and imaging on 16 WSRT pointings, roughly corresponding to one Apertif observation) can be done within one hour on one Happili node. Using all nodes would reduce this to 20 minutes (the time required for a single field).
