A 6.3-h superhump in the cataclysmic variable TV Columbae: the longest yet seen

We present results from a two-week multi-longitude photometric campaign on TV Col held in 2001 January. The data confirm the presence of a permanent positive superhump found in re-examination of extensive archive photometric data of TV Col. The 6.3-h period is 15 per cent longer than the orbital period and obeys the well-known relation between superhump period excess and binary period. At 5.5 h, TV Col has an orbital period longer than any known superhumping cataclysmic variable and, therefore, a mass ratio which might be outside the range at which superhumps can occur according to the current theory. We suggest several solutions for this problem.