High Mass X-ray Binaries consist of a neutron star or black-hole accreting material from its early-type, massive, stellar companion. The donor star can either be a Be star where accretion is occurred through an accretion disk or a supergiant (sgHMXB) where the compact object orbits close to its companion and accretes directly from its wind. A hidden population of obscured sgHMXBs has been revealed thanks to INTEGRAL. XMM-Newton and INTEGRAL observations of IGR J17252-3616 has shown that the absorbing column density (NH) is highly variable. The variability of NH has been interpreted as the effect of a slow and moderate wind together with a 'hydrodynamical' tail trailing the neutron star. This hypothesis is supported by hydrodynamical simulations optimized for this system. The mass of the neutron star can be estimated as a by-product of the simulations. In addition, serendipitous observations of a Be/X-ray binary located in the Large Magellanic Cloud, during a giant outburst, allowed us to study and constrain the geometry of the accretion disk.