2+ planets around HU Aquarii

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Re: 2+ planets around HU Aquarii

Post by ThinkerX on 15th September 2014, 8:41 pm

We present new eclipse observations of the polar (i.e. semi-detached magnetic white dwarf + M-dwarf binary) HU Aqr, and mid-egress times for each eclipse, which continue to be observed increasingly early. Recent eclipses occurred more than 70 seconds earlier than the prediction from the latest model that invoked a single circumbinary planet to explain the observed orbital period variations, thereby conclusively proving this model to be incorrect. Using ULTRACAM data, we show that mid-egress times determined for simultaneous data taken at different wavelengths agree with each other. The large variations in the observed eclipse times cannot be explained by planetary models containing up to three planets, because of poor fits to the data as well as orbital instability on short time scales. The peak-to-peak amplitude of the O-C diagram of almost 140 seconds is also too great to be caused by Applegate's mechanism, movement of the accretion spot on the surface of the white dwarf, or by asynchronous rotation of the white dwarf. What does cause the observed eclipse time variations remains a mystery.

Wild shot in the dark: Maybe exoplanet plus very large exomoon...or more than one? Maybe some sort of double planet?

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Re: 2+ planets around HU Aquarii

Post by Lazarus on 19th December 2014, 2:39 pm

Goździewski et al. "The HU Aqr planetary system hypothesis revisited"
http://arxiv.org/abs/1412.5899

Coplanar 2-planet systems ruled out and 3-planet architectures seem to require high mutual inclinations and retrograde orbits. Applegate mechanism is still a viable explanation for the timing variations, apparently the associated luminosity variations would be smoothed out and be hardly observable. Possibly GAIA astrometry could resolve the issue.
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