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The Data-reduction Pipeline for the INT Wide Field Camera

The Data-reduction Pipeline for the INT Wide Field Camera. Jim Lewis and Guy Rixon Cambridge Astronomy Survey Unit. The pipeline is:. The software package wfcred. Designed for CCD data from the INT WFC. Adaptable to other ING imagers; probably to imagers of other observatories.

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The Data-reduction Pipeline for the INT Wide Field Camera

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  1. The Data-reduction Pipelinefor the INT Wide Field Camera Jim Lewis and Guy Rixon Cambridge Astronomy Survey Unit

  2. The pipeline is: • The software package wfcred. • Designed for CCD data from the INT WFC. • Adaptable to other ING imagers; probably to imagers of other observatories. • Runnable on general-purpose computers. • Minimally dependent on specialised s/w infrastructure.

  3. The process • Steps shown in yellow are already supported by wfcred. • Steps shown in red will be supported soon. • Most steps need operator intervention.

  4. Introduction to wfcred • Developed by JRL with input from Peter Bunclark (IoA), Mike Irwin (CASU) and Robert Greimel (ING). • Designed to have minimal user interaction. • Work is done by IRAF: mscred plus several home grown applications in C, SPP and cl. • Command line as well as Perl/Tk user interfaces.

  5. WFCRED Components • Two components • caltool & calcombine: • Does combinations of bias and flat frames • caltool allows for some user interaction • process: • Processes target frames with no user interaction

  6. What wfcred does now (1) • Give each frame a rough WCS • Calculated from RA, Dec, aperture offsets, rotator angle and known camera geometry • Good to 5-10 arcsec (usually) • Linearise the data • WFC detectors arenot linear. • Interpolate to remove bad rows/columns

  7. What WFCRED does now (2) • Bias subtract • Either a constant or a mean bias frame • Flat field division • mscred does a "gain correction" at this stage • Image detection • Uses an algorithm similar to the APM image detection programs • This is not the final image-catalogue!

  8. What WFCRED does now (3) • Proper WCS definition • X,Y positions taken from objects detected in the previous step • Equatorial coordinates of standards taken from: • catalogues of APM scans of POSS1 or UKST plates (via the internet); • locally held GSC FITS table; • any other locally-held FITS table; • a combination of these. • Uses IRAF's ZPX projection. • Internal accuracy generally 0.3'' or better. (Target 100mas)

  9. What WFCRED does now (4) • Defringing • Mean fringe frames are either: • Formed from current set of target frames • Chosen from previously defined mean fringe frames • Fringes are removed by scaling the mean fringe frames to each individual target frame. • Defringing is automatic once fringe-frames are chosen or generated.

  10. What WFCRED will do soon • Catalogue generation: • Generate image lists. • Image Classification. • Improved WCS definition.

  11. Order of processing • Pipeline processes all frames found in the as one current working directory as one job: typically data from 7 nights of observations. • wfcred sorts frames into families by CCD number and filter. • Each family uses the same calibration frames. • Wfcred processes each family to completion before starting on the next. • This makes the most-efficient use of IRAF.

  12. Parallelism • Runs on uni-processors, multi-processors, Beowulf clusters. • Parallelism in units of one “family” of frames: each call to IRAF can go to separate processor.

  13. Areas of Difficulty • Poorly characterised detectors • Poorly defined meta-data • Poorly defined end product • Lack of observing protocol

  14. Poorly Characterised Detectors • Non-linearity in WFC "detectors". • Dud pixels

  15. Poorly Defined Meta-data • Headers are incomplete, inconsistent or wrong a certain percentage of the time. • Pipelines and archives are header driven. • Means that a preprocessor is sometimes required.

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