Levelsof γ-ray absorption due to pair production with stellar photons as predicted by the numerical model outlined by Dubus (2006). Top panel: expected γ-ray transmission as afunction of photon energy for Cir X-1 assuming an inclination i = 66° and using the best-fit ephemeris derived by Jonker et al. (2007), which is appropriate for a mid-B supergiant companion. The individual curves correspond to the orbital phases of the first (blue dashed), second (red dot-dashed), and third (black solid) H.E.S.S. observation intervals. Bottom panel: expected γ-ray transmission for V4641 Sgr as a function of orbital phase derived using the orbital solution of Orosz et al. (2001) and assuming a circularised orbit. The individual curves represent photon energies of 10 GeV (black solid), 1 TeV (blue dashed), and 10 TeV (red dot-dashed). Vertical lines indicate the first (dot-dashed) and second (dashed) H.E.S.S. observation epochs.