# 5.4 Photometric processing

Author(s): Giorgia Busso, Francesca De Angeli, Dafydd W. Evans, Paolo Montegriffo

Once obtained the AstroElementaries from IDT (Section 5.2) and the integrated flux $G_{\rm BP}$ and $G_{\rm RP}$ from the BP/RP processed epoch spectra (Section 5.3), the last procedure that needs to be applied to the epoch photometry is the calibration. The following section describes how to obtain the calibrations from a selected set of well behaved sources. The internal calibration (Section 5.4.1) is then applied to all sources to obtain their epoch internally calibrated photometry, i.e. all the observations for a certain source belong to the same photometric system and they can then be averaged to obtain the source mean photometry in the Gaia system. Finally the external calibration (Section 5.4.1) transforms these fluxes into absolute magnitudes.

Note that once obtained the calibrated epoch photometry, not all observations are always used in the accumulation to form the mean photometry: a set of filters were applied to avoid noisy data, for instance those affected by CCD defects. A complete list of the filters applied is provided by Riello et al. (2020).