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Pipeline Version Log

Description of pipeline software updates

Pipeline v. 1

  • Images: stacking bug causing non-linearity in stacked images.
  • Catalogues: missing Petrosian, Kron and Hall fluxes, all flux errors and coordinate errors.
  • Calibration: 2MASS old colour equations.

Pipeline v. 2 (EDR)

  • Images: stacking bug fixed, improved sky correction.
  • Catalogues: full standard parameter set - note that this does not include PSF and Sersic profile fits.
  • Calibration: 2MASS new colour equations. Systematic 0.04 mag offset in H-band in 2MASS is now removed as well (see Simon Hodgkin's photometric calibration document for more details).

Pipeline v. 3 (DR1)

  • Images: same as v. 2 plus cross-talk correction and improved sky correction. The new correction reduced the cross talk effect by a factor of ~10. The new sky correction is now grouping the MSBs on exposure time when forming the sky frames.
  • Catalogues: same as v. 2.
  • Calibration: same as v. 2.

Pipeline v. 4

More robust front-end to deal with missing files and nulls (blank images).
PSF fitting slow progress, but major problems have hopefully been fixed. It will improve astrometry as well.
Persistence has been investigated, removal is impractical and impact should be negligible.

  • Images: Improved sky subtraction: the algorithm now groups master skies by time and MSB, if possible, and makes better use of all potential sky data.
  • Catalogues: same as v. 2. The software has been upgraded to generalise image detection and remove internal quantisation problem.
  • Calibration: restricted colour range to 0 < (J-Ks) < 1. Added photometric error on the per-pointing photometric zero point. Added nightly average zero point and scatter per filter. Re-investigating Y and Z calibration including Galactic extinction correction terms.

Pipeline v. 5

  • Images: Improved cross-talk correction to make it more robust in regions of complex nebulosity, where it had previously introduced some extra negative artefacts.
  • Catalogues: A simple robust variant on Maximum Likelihood centroiding has been developed and implemented. This adds minimal overhead to the processing but yields to a 50% improvement in individual object rms astrometry, yielding close to optimal centroiding for both stars and galaxies. This will enable a better (up to a factor of 2) astrometric precision for proper motion measurements.
  • Calibration: same as v. 4. Still awaiting the final offsets from the photometry working group for the Y- and Z-band calibration. This is to ensure that A0 stars have zero colour in all WFCAM broadbands.
  • Astrometry: astrometric calibration is now using wavebad-specific distortion terms (Z -44.0; Y -45.0; J -46.0; H -50.0; K -60.0). The improvement in the systematic errors (~< 25 mas rather than ~< 75mas) is probably not needed for many applications but it will lead to improved proper motion estimates, particularly when different bandpasses are used for different epochs.