  From optical high-resolution spectra the nature of the unseen companion of HW
Vir is determined without detection of any spectral features originating from
the secondary itself. Using radial velocity measurements from the primary hot
subdwarf B star and from weak additional absorption lines detected close to the
secondary eclipse, probably caused by reflected light off the surface of the
secondary, the mass and radius of the companion is determined. The values are
consistent with those of a M type main sequence star.
