V729 Sgr: a long period dwarf nova showing negative superhumps during quiescence

Abstract

We report K2 observations of the eclipsing cataclysmic variable V729 Sgr which covered nearly 80 d in duration. We find five short outbursts and two long outbursts, one of which shows a clear plateau phase in the rise to maximum brightness. The mean time between successive short outbursts is ∼10 d while the time between the two long outbursts is ∼38 d. The frequency of these outbursts is unprecedented for a cataclysmic variable (CV) above the orbital period gap. We find evidence that the mid-point of the eclipse occurs systematically earlier in outburst than in quiescence. During five of the six quiescent epochs we find evidence for a second photometric period which is roughly 5 per cent shorter than the 4.16 h orbital period which we attribute to negative superhumps. V729 Sgr is therefore one of the longest period CVs to show negative superhumps during quiescence.