Distribution of F2. Top panel: distribution for the full sample, adopting 0.09 km s⁻¹ as the typical error on HERMES radial-velocity measurements. Bottom panel: stellar mass vs. F2 (see Eq. (4)) for APOGEE and HERMES data combined. The threshold for binarity has been set at F2 > 3. The symbols follow the classification of Fig. 1 (when the star is considered as a binary, its symbol is enclosed within a square). Stars with F2 ≥ 4 are displayed at F2 = 4.