KIC 9406652: A laboratory for tilted disks in cataclysmic variable stars. II. Modeling of the orbital light curves

TL;DR

This study models the orbital light curves of the dwarf nova KIC 9406652 to confirm the presence of a tilted, precessing accretion disk, constraining system inclination and disk tilt angles through numerical simulations.

Contribution

It provides the first successful numerical modeling of orbital light curves in a tilted disk system, confirming the tilted disk hypothesis and estimating key system parameters.

Findings

Reproduced observed orbital light curves with a simple irradiation model.

Estimated binary inclination angle as approximately 45 degrees.

Constrained the disk tilt angle to about 2 degrees.

Abstract

KIC 9406652, one of the recently identified IW And-type dwarf novae, is the best target for studying the tilted disk in cataclysmic variable stars. In a previous paper by Kimura, Osaki, and Kato (2020), we analyzed its Kepler light curves and found that its orbital light curves during the brightening stage were dominated by the reflection effect of the secondary star and varied with the orientation of the tilted disk; the amplitude was maximized at the minimum of the super-orbital signal and the phase of the light maximum shifted to an earlier one with the advance of the super-orbital phase. We argued there that this was the direct evidence of the retrogradely precessing tilted disk as the secondary star acts like a reflecting object. In order to confirm this interpretation, we have performed numerical modeling of orbital light curves in this paper. We have succeeded in reproducing the main characteristics of the observed orbital light curves by a simple model in which the secondary star is irradiated by the tilted disk. We have also constrained the inclination angle, $i$, of the binary system and the tilt angle, $\theta$, of the disk purely from photometric considerations. The best-fitting parameter set is found to be $i \sim$45~deg and $\theta \sim$2.0~deg, respectively. The orbital inclination thus estimated is consistent with that obtained from the spectroscopic considerations within the uncertainty limit. On the other hand, the tilt angle of the disk could be underestimated by using only the semi-amplitude of super-orbital signals.