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gaia data release 3 documentation

5 Photometric data

5.2 Pre-processing

Author(s): Francesca DeAngeli, Giorgia Busso

The ingestion and pre-processing activities include a number of steps that are necessary for any further processing of the data.

The ingestion phase in particular converts the data as received by the DPC into a data format that is designed and optimized for the photometric processing. This requires matching information contained in different tables using the available cross-match information.

Bias correction and computation of predicted positions are important modules in the pre-processing stage. Bias correction for the SM and AF observations is taken care within the IDU pre-processing (see Section 3.3.2). Only GBP and GRP observations need to be corrected for bias in PhotPipe. This is done using the same algorithm and software as the one used in IDU, which relies on the aforementioned CCD PEM NU library.

Predicted positions of sources at the time of observation are required for the calibration of flux loss and of the geometry of the BP/RP instruments. The computation of predicted positions at the desired accuracy requires the availability of astrophysical coordinates for all sources at a higher accuracy than what is normally available from ground. For Cycle 03, these were computed from the results of the AGIS processing.

Finally, also the scaling for the different gate observation time (see Section 1.1.3) is executed, so that the final product is a spectrum in electrons per second, ready to be processed, as described in the following section.