Spectroscopy of the roAp star Alpha-Cir -- II. The bisector and   equivalent-width of the H-alpha line
  We present bisector measurements of the H-alpha line of the rapidly oscillating Ap (roAp) star, Alpha-Cir, obtained from dual-site observations with medium-dispersion spectrographs. The velocity amplitude and phase of the principal pulsation mode vary significantly, depending on the height in the H-alpha line, including a phase reversal between the core and the wings of the line. This supports the theory, suggested in Paper I, of a radial pulsational node in the atmosphere of the star. Blending with metal lines partially affects the H-alpha bisector results but probably not enough to explain the phase reversal.   We have also detected changes in the equivalent-width of the line during the pulsation, and measured the oscillatory signal as a function of wavelength across the H-alpha region. 
I. K. Baldry, M. Viskum, T. R. Bedding, H. Kjeldsen, S. Frandsen