Monitoring the hydrogenic column density in obscured HMXB

We request to monitor 4 obscured HMXB composed by a neutron star and asupergiant OB companion (IGR J163204751, IGR J163934643, IGR J164184532, IGRJ180272016 in order of preference) in order to study their spectral evolutionalong their orbital period, particularly the hydrogenic column density. We planto observe IGR J163204751 8 times 5 ks and IGR J163934643, IGR J164184532 andIGR J180272016 5 times 7 ks for a total of 145 ks. Because of the stronginteraction between the supergiant wind and the Xray radiation of the accretedmaterial, these sources are ideal laboratories to study the relation between thecolumn density and the orbital period and derive the properties of the stellarwind. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]