5.2.1 Overview

Author(s): Francesca De Angeli

The PhotPipe system running at DPCI is currently registered as consumer of 248 different data types. Even though not all types are currently in use, this figure gives a fair idea of the complexity of the data handling and of combining all the various inputs to produce the PhotPipe final products. Here follows a list of the main inputs, without these no processing could be performed:

  • Raw observations (Astro- and PhotoObservations, AO and PO respectively), containing the decoded telemetry. These are produced on a daily basis in IDT for all FoV transits.

  • Object logs, containing a minimal record of the detection features, such as time, coordinate, FoV, acquisition mode, etc. and the brightness of the source observed in a transit. These are needed for the application of the bias calibration which is done in PhotPipe for the BP/RP data.

  • CCD PEM NU library, produced off-line in Edinburgh, required for the application of the bias calibration. Full mitigation is applied in PhotPipe.

  • IDT/IDU data products, in particular AstroElementaries (AE), containing the results of the Image Parameter Determination, IPD. For Cycle 02 processing only IDU results were used. IPD performs a fit to the samples for each CCD transit to produce an estimate of the centroid position (AL only for 1D windows) and of the integrated flux. For this it uses a library of LSF/PSF that is computed off-line (Section 2.3.2). The library used in IDU during Data Segments 00, 01 and 02 did not include dependencies in AC motion, colour or time.

  • Cross-match information, linking each transit either to a source existing in the current source catalogue (i.e. the catalogue of the sources detected by Gaia) or to a new source. There are two sources of cross-match data: IDT, which runs a cross-match on a daily basis, and IDU, which runs at the end of each Data Segment covering all data since the start of nominal operations. IDU has the advantage of being able to use multi-epoch information to improve the results and to filter more efficiently spurious observations. So far PhotPipe has always relied on the most recent IDU cross-match results.

  • Satellite attitude, required to reconstruct the satellite position and pointing direction at any time. There are three systems producing attitude: IDT does a daily attitude reconstruction (OGA1, Section 2.4.5), ODAS (Section 2.4.5) improves this on a daily basis while AGIS runs in the cyclic processing to provide the best attitude reconstruction (OGA3, Section 3.3.5). PhotPipe requires the accuracy reached by OGA3 for the prediction of centring errors (for the flux loss calibration) and predicted positions (for the geometric calibration of the BP/RP instruments and for the special treatment of observations in crowded areas).

  • Source astrophysical coordinates, required to compute predicted positions of the sources onto the focal plane (for measuring centring errors and calibrating the geometry of the BP/RP instruments). ODAS produces these on a daily basis for a fraction of the sources. For Cycle 02 AGIS astrometry was available for all sources.

  • AF geometric calibration, required for the computation of predicted positions of sources on the BP/RP CCDs (see the description of the previous item in this list).

The careful reader will notice that the above list does not include an external source catalogue. This is because for Cycle 02, PhotPipe did not rely on any bootstrap information for the observed sources. No external catalogue is ever used for the processing of the data. External catalogues are currently only used for validation purposes and are only listed in the validation (see Section 5.5).

For a detailed report on the number of input data for Cycle 02, please refer to the DPCI Processing Configuration section at Section 1.3.4.