Astrometrically selected candidate members of the W40 population, superimposed on a Spitzer 4.5 μm image of the region. The size is 40′×40′ (5.84 × 5.84 pc² projected at the distance of W40). Blue triangles are the high-confidence members having μ_rel < 2 mas yr⁻¹, 1.8 < π(mas) < 2.2, σ(π) < 0.2 mas, RUWE < 1.4 listed in Table 1. Green squares are the candidate members having μ_rel < 0.2 mas yr⁻¹, 1.0 < π(mas) < 3.0 with no restriction on the precision of the parallax or the quality of the astrometric solution listed in Table 2. The red circles indicate the stars for which we obtained visible spectroscopy as described in Sect. 3.