SIMBAD references

An observation of the X-ray binary system Her X-1/HZ Her by the AstroSat UltraViolet Imaging Telescope (UVIT) was carried out in 2018. The observation was taken with the far ultra-violet (FUV) camera of UVIT with the CaF₂ filter (125-175 nm band) and lasted ≃0.6 of one binary orbit. Her X-1 was in the late main high state at 35 day phase ≃0.20. Clear orbital modulation of the UVIT light curve is seen, showing egress from eclipse of the neutron star and double-peak shape half an orbital period later. The FUV emission from Her X-1 is shown to arise partly from the accretion disk and partly from the X-ray heated face of Hz Her. We carry out modeling of the system using the Shape code and fit the FUV light curve. New constraints are obtained for the geometric parameters of the tilted and twisted accretion disk around the neutron star, and improvements to the basic disk model are suggested.