We have studied the short cadence Kepler light curve of an SU UMa star , V1504 Cyg , which covers a period of \sim 630 d. All superoutbursts in V1504 Cyg have turned out to be of precursor-main types , and the superhump first appears near the maximum of the precursor .
The superhumps grow smoothly from the precursor to the main superoutburst , showing that the superoutburst was initiated by a tidal instability ( as evidenced by the growing superhump ) as envisioned in the thermal-tidal instability ( TTI ) model proposed by Osaki ( 1989 , PASJ , 41 , 1005 ) .
We performed a power spectral analysis of the light curve of V1504 Cyg .
One of the outstanding features is the appearance of a negative superhump extending over around 300 d , well over a supercycle .
We found that the appearance of the negative superhump tends to decrease the frequency of occurrence of normal outbursts .
Two types of supercycles are recognized in V1504 Cyg , which are similar to those of the Type L and Type S supercycles in the light curve of VW Hyi , a prototype SU UMa star , introduced by Smak ( 1985 , Acta Astron. , 35 , 357 ) .
It is found that the Type L supercycle is the one accompanied by the negative superhump , and Type S is that without the negative superhump .
If we adopt a tilted disk as an origin of the negative superhump , two types of the supercycles are understood to be due to a difference in the outburst interval , which is in turn caused by a difference in mass supply from the secondary to different parts of the disk .
The frequency of the negative superhump varies systematically during a supercycle in V1504 Cyg .
This variation can be used as an indicator of the disk-radius variation , and we have found that the observed disk-radius variation in V1504 Cyg fits very well with a prediction of the TTI model .