Significance on the proper motions vs. the parallaxes for the full sample of Gaia sources within 1 deg of the NGP, all brighter than G <  20 mag. In the inset we show the classifications of the full sample of zero proper motion sources (defined as S/N_μ <  2; dotted line), where red dots and grey squares denote quasars and star symbols represent the stellar contaminants. The grey-shaded regions show the additional proposed criterion (see Sect. 4.3), requiring parallaxes to be consistent with zero (within 2σ). It is clear that imposing this additional criteria would exclude a large fraction (12/41 ∼ 30%) of the confirmed stellar sources.