Abstract
The analysis of two high resolution spectra of the Hg Mn star HD 159975 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal variations of the far-ultraviolet flux over a 18 yr time interval. From its effective temperature and surface gravity, HD 155975 appears to have evolved away from the Main Sequence in a theoretical Hertzsprung Russell diagram. It is one of the rare subgiant HgMn stars. Several Si ii resonance or low excitation lines are strong absorbers in the mean high resolution SWP spectrum of HD 159975. The Al ii resonance line at 1670.79 Å is a strong absorber too. There is no evidence of real variations of the low excitation Si ii lines.
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