2000MNRAS.318..974J

High-speed spectroscopy of two pulsating subdwarf B stars, KPD 2109+4401 and PB 8783, is presented. Radial motions are detected with the same frequencies as reported from photometric observations and with amplitudes of ∼2km.s^–1 in two or more independent modes. These represent the first direct observations of surface motion arising from multimode non-radial oscillations in subdwarf B stars. In the case of the sdB+F binary PB8783, the velocities of both components are resolved; high-frequency oscillations are found only in the sdB star and not the F star. There also appears to be evidence for mutual motion of the binary components. If confirmed, it implies that the F-type companion is ≳1.2 times more massive than the sdB star, while the amplitude of the F-star acceleration over 4h would constrain the orbital period to lie between 0.5 and 3.2d.