8.1.4 Photometry

The comparison of Gaia EDR3 photometry to external catalogues shows that issues are mainly seen in the bright end, i.e. brighter than 5-6 mag, and in $G_{\mathrm{RP}}$ for $G_{\mathrm{RP}}$ fainter than 18 mag.

Comparison with GOG simulations (Section 8.3) shows that at high latitudes the values of $G_{\mathrm{BP}}-G_{\mathrm{RP}}$ forGOG20 and Gaia EDR3 are in good agreement, but not at bright magnitudes where the colour determination seems to be problematic; however, this discrepancy is slightly reduced compared to Gaia DR2.

Results of comparison with CALSPEC are globally better than for Gaia DR2 except for $G_{\mathrm{RP}}$, which does not go through zero and confirms the magnitude dependence seen in the Hipparcos comparison. This is inside the expected uncertainties of the libraries and is not considered problematic.

The pattern of the ecliptic that was present in Gaia DR2 for sky maps of sources with phot_bp_rp_excess_factor lower than $5$ is not longer visible, meaning that the background due to zodiacal light has been successfully removed.

The phot_bp_rp_excess_factor values are improved with respect to Gaia DR2 mainly for faint sources

Comparison between mean $G$ magnitudes provided in the Gaia DR2 and Gaia EDR3 catalogues for a sample of 140,635 sources classified as RR Lyrae stars shows that 2044 sources have a difference in magnitudes more than 0.5 mag, with the Gaia EDR3 magnitudes being fainter (Section 8.6, Figure 8.29). Most of these sources seem to be extended objects.

Median differences between Gaia DR2 and Gaia EDR3 photometry in open clusters are very small (Section 8.7), i.e. -0.0087 ($G$), 0.0027 ($G_{\mathrm{BP}}$), 0.0074 ($G_{\mathrm{RP}}$), 0.0074 ($G_{\mathrm{BP}}-G_{\mathrm{RP}}$), with dispersions of the order of 0.01-0.02 in $G$, $G_{\mathrm{BP}}$, $G_{\mathrm{BP}}-G_{\mathrm{RP}}$ and lower in $G_{\mathrm{RP}}$. However, for a small sample of stars differences can be higher than 1.5-1.7 mag in $G_{\mathrm{BP}}$ and $G$, possibly related with the small number of observations ().

Photometry in crowded fields (globular clusters, Section 8.7) is still worse than in non crowded regions, with deviations both in colour and in magnitude already present at phot_bp_rp_excess_factor $>2$.