# 8.2.1 Source selection

Author(s): René Andrae, Morgan Fouesneau, Coryn Bailer-Jones

For Gaia DR2, only sources down to apparent magnitude $G\leq 17$ have been processed. For sources fainter than that, we do not expect that reliable parameter estimates could be provided.

Some sources have compromised photometry, seen from the fact that they deviate from the standard locus of stars (i.e. that where most stars lie) by significantly more than expected from the flux uncertainties. We therefore introduce quality cuts, shown in Figure 8.2. Only sources which fall into the standard ‘banana-shaped’ region are considered as ‘good’ data. Nevertheless, all sources are processed and bad photometry is indicated by a flag (see Section 8.2.2).

Likewise, some sources have missing or non-positive parallaxes. For these, we can only estimate effective temperatures (see Section 8.3.1) but no extinctions and no luminosities or radii. Missing astrometry is indicated by a flag (see Section 8.2.2).