1305.5877 (Yoji Osaki et al.)

Study of Superoutbursts and Superhumps in SU UMa Stars by the Kepler Light Curves of V344 Lyrae and V1504 Cygni    [PDF]

Yoji Osaki, Taichi Kato

We study the short cadence Kepler public light curves of SU UMa stars, V344 Lyr and V1504 Cyg extending for a period of well over two years by using power spectral analysis. We have determined the orbital period of V344 Lyr to be Porb=0.087903(1) d. We have reanalyzed the frequency variation of the negative superhump in a complete supercycle of V1504 Cyg with additional data of the O-C diagram, confirming its characteristic variation in accordance with the thermal tidal instability model. We present a new two-dimensional period analysis based on a new method least absolute shrinkage and selection operator (Lasso). The new method gives very sharp peaks in the power spectra and it is very useful for the study of frequency variation in cataclysmic variable stars. We have analyzed simultaneous frequency variation of the positive and negative superhumps. If appropriately converted, it is found that they vary in unison, indicating that they represent the disk radius variation. We have studied the frequency (or period) variations of the positive superhumps during superoutbursts. These variations are understood in a qualitative way by a combination of the disk radius variation and the variation of the pressure effects during superoutburst. A sudden excitation of oscillation with a frequency range near the negative superhump (which we call "impulsive negative superhump") was observed in the descending branch of several outbursts of V344 Lyr. These events seem to occur just prior to the next superoutburst and to act as a "lead" of the impending superoutburst.

View original: http://arxiv.org/abs/1305.5877