¹ Landessternwarte Königstuhl, D-69119 Heidelberg, Germany
² European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching b. Muenchen, Germany
³ Astronomical Institute, Academy of Sciences, CZ-25165 Ondrejov, Czech Republic
⁴ Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK

The line profile variability of  CMa is modeled for various photospheric absorption lines of different ions as non-radial pulsation. The retrograde pulsation suggested by Baade (1982) could be confirmed. Due to rapid rotation, the line profile variability appears prograde, however. The line profiles could be reproduced in great detail, including prominent structures like "spikes" and "ramps". These features arise naturally from the pole-on orientation of the star together with high-amplitude pulsation in g-modes, i.e. with horizontal motions being dominant. The change of the line profile variability during outbursts (understood as the beginning of phases of high brightness) reported in Paper II of this series can also be understood within the framework of non-radial pulsation if veiling effects of the circumstellar disk are taken into account. It is concluded that the coherent periodic line profile variability of the absorption lines of  CMa can be explained by non-radial pulsation in detail.

Accepted by A&A
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