# 2+ planets around HU Aquarii

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## 2+ planets around HU Aquarii

Detection of a planetary system orbiting the eclipsing polar HU Aqr

Another multiplanet circumbinary system.

Lazarus
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## Re: 2+ planets around HU Aquarii

Magnificent

Edasich
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## Re: 2+ planets around HU Aquarii

Have to wonder if the third planet might be giving the second planet a spurious high eccentricity - in the given configuration, the periapse of the outer planet lies within the inner planet's orbit.

Lazarus
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## Re: 2+ planets around HU Aquarii

Indeed I don't get so feasible orbital configurations with zero eccentricity inner planet and 0.5 outer second one. I find more plausible a 0.2 eccentricity for the first and 0.36 for the outer.

Unless we are dealing with slighlty non-coplanar planets as for Upsilon Andromedae (i1=90 and i2=75), perhaps.

Surely way more strange would be QS Virginis system with two highly eccentric substellar objects (if confirmed)...

Edasich
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## Re: 2+ planets around HU Aquarii

Someone should run this in some orbit simulator. Try to find a stable configuration, cause I agree it sounds quite odd.

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atomic7732
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## Re: 2+ planets around HU Aquarii

A dynamical analysis of the proposed HU Aquarii planetary system
http://arxiv.org/abs/1106.0777

It has recently been suggested that the eclipsing polar HU Aquarii is host to at least two giant planets. We have performed highly detailed dynamical analysis of the orbits of those planets and show that the proposed system is highly unstable on timescales of < 5\times 10$^3$ years. For the coplanar orbits suggested in the discovery letter, we find stable orbital solutions for the planetary system only if the outer body moves on an orbit that brings it no closer to the host star than ~ 6 AU. The required periastron distance for the outer planet lies approximately 5 Hill radii beyond the orbit of the inner planet, and well beyond the 1-{\sigma} error bars placed on the orbit of the outer planet in the discovery letter. If the orbits of the proposed planets are significantly inclined with respect to one another, the median stability increases slightly, but such systems still become destabilised on astronomically minute timescales (typically within a few 10$^4$ years). Only in the highly improbable scenario where the outer planet follows a retrograde but coplanar orbit (i.e. inclined by 180 degrees to the orbit of the inner planet) is there any significant region of stability within the original 1-{\sigma} orbital uncertainties. Our results suggest that, if there is a second (and potentially, a third planet) in the HU Aquarii system, its orbit is dramatically different to that suggested in the discovery paper, and that more observations are critically required in order to constrain the nature of the suggested orbital bodies.

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Sirius_Alpha

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## Re: 2+ planets around HU Aquarii

The HW Virginis system also looks like it will be unstable. NN Serpentis is probably in resonance which might help in that case.

Lazarus
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## Re: 2+ planets around HU Aquarii

Revisiting the proposed planetary system orbiting the eclipsing polar HU Aquarii
http://arxiv.org/abs/1110.2542

It has recently been proposed, on the basis of eclipse-timing data, that the eclipsing polar cataclysmic variable HU Aquarii is host to at least two giant planets. However, that result has been called into question based upon the dynamical stability of the proposed planets. In this work, we present a detailed re-analysis of all eclipse timing data available for the HU Aquarii system, making use of standard techniques used to fit orbits to radial-velocity data. We find that the eclipse timings can be used to obtain a two-planet solution that does not require the presence of additional bodies within the system. We then perform a highly detailed dynamical analysis of the proposed planetary system. We show that the improved orbital parameters we have derived correspond to planets that are dynamically unstable on unfeasibly short timescales (of order 10^4 years or less). Given these results, we discuss briefly how the observed signal might in fact be the result of the intrinsic properties of the eclipsing polar, rather than being evidence of dynamically improbable planets. Taken in concert, our results highlight the need for caution in interpreting such timing variations as being planetary in nature.

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Sirius_Alpha

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## Re: 2+ planets around HU Aquarii

No more in the list *sigh*

Edasich
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## Re: 2+ planets around HU Aquarii

:-(

Wonder how the other circumbinary planetary systems around cataclysmic variables (and pre-cataclysmic variables) will hold up.

Lazarus
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## Re: 2+ planets around HU Aquarii

Wonder if it will come back with alternative solution as for NN Serpentis.

Edasich
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## Re: 2+ planets around HU Aquarii

At least DP Leonis (AB)b has survived one round of reanalysis, hopefully some of the eclipse-timed systems are genuine planets.

Lazarus
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## Re: 2+ planets around HU Aquarii

Maybe we shouldn't forget about the second planetary companion to HU Aqr just yet...

New Light-Travel Time Models and Orbital Stability Study of the Proposed Planetary System HU Aquarii
http://arxiv.org/abs/1112.0066

In this work we propose a new orbital architecture for the two proposed circumbinary planets around the polar eclipsing binary HU Aquarii. We base the new two-planet, light-travel time model on the result of a Monte Carlo simulation driving a least-squares Levenberg-Marquardt minimisation algorithm on the observed eclipse egress times. Our best-fitting model with $\chi_{r}^2=1.43$ resulted in high final eccentricities for the two companions leading to an unstable orbital configuration. From a large ensemble of initial guesses we examined the distribution of final eccentricities and semi-major axes for different $\chi_{r}^2$ parameter intervals and encountered qualitatively a second population of best-fitting parameters. The main characteristic of this population is described by low-eccentric orbits favouring long-term orbital stability of the system. We present our best-fitting model candidate for the proposed two-planet system and demonstrate orbital stability over one million years using numerical integrations.

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Sirius_Alpha

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## Re: 2+ planets around HU Aquarii

I said it was not to disprove so quickly...

Edasich
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## Re: 2+ planets around HU Aquarii

HU Aqr c is back from the dead on the EPE.
http://exoplanet.eu/star.php?st=HU+Aqr(AB)

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Sirius_Alpha

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## Re: 2+ planets around HU Aquarii

Next to "re-animate" is QS Virginis. A new solution has been provided though a bit... "weird".

Edasich
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## Re: 2+ planets around HU Aquarii

Might be time to return HU Aqr c to the grave.

The Curious Case of HU Aquarii - Dynamically Testing Proposed Planetary Systems
http://arxiv.org/abs/1201.5730

From the paper:
At the timescale considered here, with timing variations occurring over thousands of days, the most likely non-planetary explanation for the observed signal results from the behaviour of the secondary star in the system, the M dwarf. With a fast rotation period of order a few hours (a result of the star being tidally locked in its rotation about the primary, the white dwarf), the dynamo effect within the M dwarf would be expected to be large. If we assume that the stars in such stellar systems display a magnetic cycle similar to the Sun’s double peaked 22-year cycle, the distribution of angular momentum between the two will change over time. This will, in turn, have the effect of modifying the shape of the secondary star, with the knock-on effect of affecting the gravitational interaction between the primary and secondary, and hence the orbital period of the pair

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Sirius_Alpha

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## Re: 2+ planets around HU Aquarii

Sirius_Alpha wrote:Might be time to return HU Aqr c to the grave.

The Curious Case of HU Aquarii - Dynamically Testing Proposed Planetary Systems
http://arxiv.org/abs/1201.5730

From the paper:
At the timescale considered here, with timing variations occurring over thousands of days, the most likely non-planetary explanation for the observed signal results from the behaviour of the secondary star in the system, the M dwarf. With a fast rotation period of order a few hours (a result of the star being tidally locked in its rotation about the primary, the white dwarf), the dynamo effect within the M dwarf would be expected to be large. If we assume that the stars in such stellar systems display a magnetic cycle similar to the Sun’s double peaked 22-year cycle, the distribution of angular momentum between the two will change over time. This will, in turn, have the effect of modifying the shape of the secondary star, with the knock-on effect of affecting the gravitational interaction between the primary and secondary, and hence the orbital period of the pair

Perhaps not. This abstract dates back September 2011. The new orbital solution is more recent (Dec 01/2011).
And it yet displays the old orbital solution.

Edasich
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## Re: 2+ planets around HU Aquarii

On the HU Aquarii planetary system hypothesis

Further analysis of the data considering different time resolutions, the effect of observing in different spectral windows and consideration of dynamical stability. Seems the best model is a 1-planet system, a ~7 Jupiter mass planet in a low-eccentricity orbit at 4.3 AU.

Lazarus
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## Re: 2+ planets around HU Aquarii

http://exoplanet.eu/star.php?st=HU+Aqr%28AB%29

EPE update is weird, they've put the 4.3 AU single planet as "unconfirmed" but left the second planet of the two-planet solution as confirmed...

Lazarus
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## Re: 2+ planets around HU Aquarii

Not first time and not last but re-analysis concludes better fit for 1 planet

tommi59
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## Re: 2+ planets around HU Aquarii

Investigating AM Her Cataclysmic Variables with OPTIMA
http://arxiv.org/abs/1210.0884

...The new observations of HU Aqr confirm that the O--C (Observed minus Calculated) diagrams exhibit variations known for this binary which can be explained by a single, massive Jupiter--like planet, possibly accompanied by a very distant companion.

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Sirius_Alpha

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## Re: 2+ planets around HU Aquarii

More on the ambiguity of the HU Aqr system with more data.

On the ephemeris of the eclipsing polar HU Aquarii
http://arxiv.org/abs/1403.4160

The magnetic cataclysmic variable HU Aquarii displayed pronounced quasi-periodic modulations of its eclipse timing. These were interpreted in terms of the light-travel time (LTT) effect caused by a circumbinary planet or planetary system. We report new photometric observations that revealed another precise eclipse timing for the October 2013 epoch, the first obtained in a high accretion state after many years in low or intermediate states. The eclipse was observed to occur earlier by 95.3 +- 2.0 s or 62.8 +- 2.0 s than expected for an assumed linear or quadratic ephemeris, respectively. The implied apparent strong evolution of the orbital period calls for a revision of the current planetary model or the planetary parameters. The object deserves further monitoring to uncover the true nature of the observed variability and to constrain the properties of the proposed planet or planetary system. The new observations prove that advanced amateur equipment can successfully be used in the growing field of planet search in wide circumbinary orbits via the LTT effect.

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Sirius_Alpha

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## Re: 2+ planets around HU Aquarii

Weirdness abound.

Testing the planetary models of HU Aquarii
http://arxiv.org/abs/1409.3586

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.

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Sirius_Alpha

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## Re: 2+ planets around HU Aquarii

Not looking good for the proposed planets around such systems, given that there does now seem to be some kind of intrinsic effect (or combination of effects) that can exceed the Applegate mechanism in causing period variations.

Lazarus
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