Comparison of the proposed tracks for the Vela X-1 system relative to the Vela OB1 association following Fig. 7 of van Rensbergen et al. (1996), Fig. 3 of Kaper et al. (1997), and Fig. 7 of Gvaramadze et al. (2018). The stars shown as belonging to the association (see Sect. 5.1.2) are listed in Table A.3. The numbers along the tracks indicate where the system would have been one, two, or three million years ago, based on the assumptions in these publications. The direction of proper motion, as listed in the HIPPARCOS Input Catalog (HIC) (Turon et al. 1992) and as obtained by Sahu (1992), is shown by gray vectors. The inset is adapted from Fig. 6 of Maíz Apellániz et al. (2018) and shows a 14′ × 14′ WISE RGB mosaic. Green and yellow arrows indicate the raw and corrected proper motions, respectively (see the reference for details). The vectors shown in the inset are not to scale with those of the main drawing.