KIC 9406652: A laboratory of the tilted disk in cataclysmic variable stars. (arXiv:2008.11328v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Kimura_M/0/1/0/all/0/1">Mariko Kimura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Osaki_Y/0/1/0/all/0/1">Yoji Osaki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kato_T/0/1/0/all/0/1">Taichi Kato</a>
KIC 9406652 is a cataclysmic variable (CV), sub-classified as `IW And-type
star’, showing a repetition of standstills with oscillatory variations
terminated by brightening. This system showed negative superhumps,
semi-periodic variations having periods slightly shorter than the orbital
period, and super-orbital signals, both of which are believed to originate from
a precessing, tilted accretion disk. We have re-examined its Kepler light curve
extending over 1500 d. In accordance with a cycle of the IW And-type light
variation, the frequency of negative superhumps showed a reproducible
variation: a rapid drop during the brightening and a gradual increase during
the standstill. They are interpreted as the drastic change in the radial mass
distribution and the expansion of the tilted disk, which is not expected from
the existing models for IW And stars. The constancy in flux amplitudes of
negative superhumps confirms that their light source is the bright spot
sweeping across the surface of the tilted disk. The frequencies of negative
superhumps and super-orbital signals varied in unison on long timescales,
suggesting their common origin: the tilted disk. Orbital signals at the
brightening were dominated by the irradiation of the secondary star and varied
with the orientation of the tilted disk; the amplitude was maximized at the
minimum of super-orbital signals and the light maximum shifted to early orbital
phases as the super-orbital phase advances. This is the first direct evidence
that the disk was tilted out of the binary orbital plane and retrogradely
precessing. The tilt angle of the disk inferred from semi-amplitudes of
super-orbital signals was lower than 3 degrees. The diversity in light curves
of negative superhumps supports this and suggests that a part of the gas stream
overflows the disk edge. This study thus offers rich information about the
tilted disk in CVs.
KIC 9406652 is a cataclysmic variable (CV), sub-classified as `IW And-type
star’, showing a repetition of standstills with oscillatory variations
terminated by brightening. This system showed negative superhumps,
semi-periodic variations having periods slightly shorter than the orbital
period, and super-orbital signals, both of which are believed to originate from
a precessing, tilted accretion disk. We have re-examined its Kepler light curve
extending over 1500 d. In accordance with a cycle of the IW And-type light
variation, the frequency of negative superhumps showed a reproducible
variation: a rapid drop during the brightening and a gradual increase during
the standstill. They are interpreted as the drastic change in the radial mass
distribution and the expansion of the tilted disk, which is not expected from
the existing models for IW And stars. The constancy in flux amplitudes of
negative superhumps confirms that their light source is the bright spot
sweeping across the surface of the tilted disk. The frequencies of negative
superhumps and super-orbital signals varied in unison on long timescales,
suggesting their common origin: the tilted disk. Orbital signals at the
brightening were dominated by the irradiation of the secondary star and varied
with the orientation of the tilted disk; the amplitude was maximized at the
minimum of super-orbital signals and the light maximum shifted to early orbital
phases as the super-orbital phase advances. This is the first direct evidence
that the disk was tilted out of the binary orbital plane and retrogradely
precessing. The tilt angle of the disk inferred from semi-amplitudes of
super-orbital signals was lower than 3 degrees. The diversity in light curves
of negative superhumps supports this and suggests that a part of the gas stream
overflows the disk edge. This study thus offers rich information about the
tilted disk in CVs.
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