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We analyzed a Kepler light curve of KIC 8751494, a recently recognizednovalike cataclysmic variable in the Kepler field. We detected a stableperiodicity of 0.114379(1) d, which we identified as being the binary's orbitalperiod. The stronger photometric period around 0.12245 d, which had beendetected from the ground-based observation, was found to be variable, and weidentified this period as being the positive superhump period. This superhumpperiod showed short-term (10-20 d) and strong variations in period mostunexpectedly when the object entered a slightly faint state. The fractionalsuperhump excess varied as large as ~30%. The variation of the period very welltraced the variation of the brightness of the system. The time-scales of thisvariation of the superhump period was too slow to be interpreted as thevariation caused by the change in the disk radius due to the thermal diskinstability. We interpreted that the period variation was caused by the varyingpressure effect on the period of positive superhumps. This finding suggeststhat the pressure effect, in at least novalike systems, plays a very important(up to ~30% in the precession rate) role in producing the period of thepositive superhumps. We also described a possible detection of the negativesuperhumps with a varying period of 0.1071-0.1081 d in the Q14 run of theKepler data. We also found that the phase of the velocity variation of theemission lines reported in the earlier study is compatible with the SW Sex-typeclassification. Further, we introduced a new two-dimentional period analysisusing least absolute shrinkage and selection operator (Lasso) and showedsuperior advantage of this method.

Analysis of a Kepler Light Curve of the Novalike Cataclysmic Variable KIC 8751494