Thursday, March 7, 2013

1303.1237 (Taichi Kato et al.)

Analysis of Kepler Light Curve of the Novalike Cataclysmic Variable KIC 8751494    [PDF]

Taichi Kato, Hiroyuki Maehara
We analyzed the Kepler light curve of KIC 8751494, the recently recognized novalike cataclysmic variable in the Kepler field. We detected a stable periodicity of 0.114379(1) d, which we identified as being the orbital period. The stronger photometric period around 0.12245 d, which had been detected from the ground-based observation, was found to be variable, and we identified this period as being the positive superhump period. Most unexpectedly, this superhump period showed short-term (10--20 d) and strong variations in period when the object entered a slightly faint state. The fractional superhump excess varied as large as ~30%. The variation of the period very well traced the variation of the brightness of the system. The time-scales of this variation of the superhump period was too slow for the thermal disk instability. We interpret that the period variation was caused by the varying pressure effect on the period of positive superhumps. This finding suggests that the pressure effect, at least in novalike systems, plays a very important (up to ~30% in the precession rate) role in producing the period of the positive superhumps. We also describe the possible detection of negative superhumps with varying period of 0.1071-0.1081 d in the Q14 run, and found that the variation of the frequency of the negative superhumps followed that of positive superhumps. The relation between the fractional superhump excesses of negative and positive superhumps can be understood if the positive superhumps are reduced in angular frequency due to the pressure effect. We also found that the phase of the velocity variation is compatible with the SW Sex-type classification. We also introduce a new two-dimentional period analysis using least absolute shrinkage and selection operator (Lasso) and show the advantage of this method.
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