Sketch of the binary system Vela X-1 where both radiative and gravitational effects are illustrated at three different orbital phases. The photoionization wake is represented as a disk-like structure to show both the cumulative effect along one entire orbit (the red ring) and the more localized effect (the fainter red tail) trailing the NS at the inferior conjunction. A clumpy stellar wind, not shown in the picture, may also be taken into account for a more complete scenario.