High-speed photometry of the intermediate polar V1223 Sgr.

The presently reported and analyzed 104 hr of photometry of the Intermediate Polar V1223 Sgr at 5 and 10 s time resolution were obtained during 1981 and 1982. From the various periodic brightness modulations, an orbital period of 0.140239 day, a rotation period of the primary of 794.380 s, and an orbital sideband of 849.8 s are derived. The last is only intermittently present. The 794 and 850 s oscillations are in phase coherence at maximum of the orbital brightness modulation. The contrast with AO Psc (H 2252-035), where phase coherence occurs at orbital brightness minimum, leads to a model in which the 794 s modulation results from reprocessing of X-ray beam from the axisymmetric parts of the accretion disc. The high speed brightness variations of V1223 Sgr possess two unusual properties: an intrinsic 'scintillation', in which the system may increase or decrease its brightness by 10-20 percent on time-scales of about 100 s, and excess power in the frequency range of 0.04-0.08 Hz, when compared with other active cataclysmic variables. The Intermediate Polar AO Psc shows similar behavior.