Iron line diagnostics of the stellar wind in X1908+075

Aims. X1908+075 is a supergiant X-ray binary (SgXB) system formed by an evolved OB star and a neutron star (NS) orbiting it with a 4.4-day period. In this study, we aim to characterize the stellar wind properties, constrain the system geometry, and investigate the origin and variability of the Fe Kα fluorescence line. Methods. We analyzed three HETGS observations taken at different orbital phases. We modeled the continuum using a bulk motion Comptonization ( ) model with a partial-covering absorption component. To identify statistically significant features, we performed a blind line search with Monte Carlo simulations that account for the look-elsewhere effect. We used the N_ Chandra Bmc H measurements at different orbital phases to constrain the orbital inclination and mass-loss rate through particle swarm optimization. Results. We detect Fe Kα emission in all observations, which remains statistically significant after correcting for multiple trials via Monte Carlo simulations (global p < 0.005). Tentative features include a Compton shoulder in the least absorbed observation and Fe Kβ in one observation, suggesting the presence of dense reprocessing material. However, we do not find evidence for highly ionized lines (Fe XXV, Fe XXVI). The Fe Kα flux correlates positively with the continuum flux, while its equivalent width shows an anticorrelation with both N_ H and the orbital phase, contrary to the canonical ``curve of growth'' observed in many high-mass X-ray binaries. Line broadening corresponds to velocities up to ∼ 3000 km s -1 , exceeding both the orbital and terminal wind velocities. Modeling the orbital modulation of N_ H yields an inclination i = 46 ± 3^̧irc and a donor mass-loss rate _W = (9.1 ± 1.6) M_⊙ ^ M 10^ -7 yr -1 . Conclusions. X1908+075 is a classical wind-fed SgXB in the direct accretion regime, where the NS accretes material from the donor’s dense wind without magnetic or centrifugal barriers. The observed variability in continuum and line emission reflects the inhomogeneous density and ionization structure of the stellar wind. Future high-sensitivity observations with broader orbital phase coverage will help disentangle the relative contributions of fluorescence, scattering, and ionization to the iron line diagnostics.