PERIODICITIES IN THE OPTICAL BRIGHTNESS VARIATIONS OF THE INTERMEDIATE POLAR TV COLUMBAE

We present extensive observations in the Walraven (VBLUW) photometric system of the intermediate polar TV Col over the period 1985-1988. We find, apart from the photometric variations at the three previously kn own periods, long-term brightness changes between groups of observatio ns of up to Delta B-J similar to 0.4 mag. During the periods of highes t mean brightness the source shows 1-2 mag outbursts, of which we dete cted four during our observations. No photometric variations are detec ted at the X-ray pulse period, or at its orbital or 5.2 hr period side bands. We derived a new ephemeris for the orbital period, and we deter mined arrival times of maximum light at the 5.2 hr and 4 day photometr ic periods. We are unable, using the arrival times from our own data a nd those listed in the literature for the 5.2 hr light curve, to deter mine any constant-period ephemeris to fit all the observations. We sug gest that the 5.2 hr period is in fact not stable and can vary non-mon otonically. Because the 4 day period is the beat period between the or bital period and the 5.2 hr period, this also applies to the variation s at this period. We investigate the changes in the optical light curv e as a function of the 4 day cycle and discuss their cause.