Resonant Excitation of Disk Oscillations in Two-Armed-Deformed Disks and Application to High-Frequency QPOs

Abstract

In previous papers we showed that in a one-armed deformed disks, p-mode and g-mode oscillations are resonantly excited by horizontal resonance, and applied it to high frequency QPOs observed in low mass X-ray binaries. In that model, the observed time variation of kHz QPOs is regarded as a result of a time-dependent precession of the deformation. In this paper we consider another possible cause of time variation of kHz QPOs. That is, we demonstrate that in a two-armed deformed disks, p-mode and g-mode oscillations are excited by {\it vertical resonance}, not by horizontal resonance(horizontal resonance dampens them). Furthermore, we show that in the case of vertical resonance, the frequencies of disk oscillations excited can vary with time if vertical disk structure changes with time. A brief application of these results to the time variation of observed kHz QPOs is made.Comment: 19 pages, 5 figures. To be published in PASJ 61, No.6 (2009