On the nature of the old nova CP Puppis

We report on nearly 48 hr of high speed photometry of the exnova CP Pup, obtained at Sutherland or Mount Stromlo, and 23 hr of spectroscopic coverage from Sutherland, during the period 1985–88. Analysis of the photometry and radial velocities derived from the spectroscopy gives a modulation period of 0.06143 d, free from the alias problems inherent in previous work, and identical for both photometry and spectroscopy. This period will not fit the earlier data of Warner and this, together with substantial amplitude variations in the photometric modulation, suggest the presence of more than one photometric periodicity. Measurements of the radial velocity semi-amplitude give values of $$\sim 200\,\text{km s}^{-1}$$ near the emission line centres, decreasing to $$\sim 120\,\text{km s}^{-1}$$ in the line wings, but with variations in phase across the line profile. A related V/R effect is seen. There is evidence for repetitive fine structure in the line profiles, but at a level too low to study in detail with the present spectra. If the K velocity of $$\sim 120\,\text{km s}^{-1}$$ is representative of the motion of the white dwarf, unreasonable values of the white-dwarf mass and orbital inclination are derived. No compelling evidence has emerged from the present study to suggest that CP Pup is a magnetic cataclysmic variable, although further study of the behaviour of the photometric modulation may elucidate this question.