Abstract
Photometric (B-filter) data of HZ Herculis obtained between 1972 and 1974 have been fitted by a model consisting of Roche-lobe-filling star transferring material to a neutron star via a tilted, preccessing, accretion disc. The disc inclination was found to be small, thus avoiding theoretical difficulties experienced with high-inclination discs. We compared a second set of B-fliter data obtained between 1980 and 1983 with the model predictions and found that the system's observed luminosity was lower during the period 1980–1983 than predicted. This is interpreted as a result of a reduction in the flux of X-rays incident upon the heated hemisphere of HZ Herculis; this conclusion seems confirmed by periodogram analysis of the two datasets. The 71 IUE low resolution spectra available have been uniformly extracted and examined. In addition to the expected orbital and X-ray cycle effects, we have observed short episodes when the CIV (λ1550) line is unusually strong.
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