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Post Info TOPIC: HW Virginis
Blobrana


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RE: HW Virginis
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Title: A Dynamical Analysis of the Proposed Circumbinary HW Virginis Planetary System
Authors: J. Horner, T. C. Hinse, R. A. Wittenmyer, J. P. Marshall, C. G. Tinney

In 2009, the discovery of two planets orbiting the evolved binary star system HW Virginis was announced, based on systematic variations in the timing of eclipses between the two stars. The planets invoked in that work were significantly more massive than Jupiter, and moved on orbits that were mutually crossing - an architecture which suggests that mutual encounters and strong gravitational interactions are almost guaranteed. In this work, we perform a highly detailed analysis of the proposed HW Vir planetary system. First, we consider the dynamical stability of the system as proposed in the discovery work. Through a mapping process involving 91,125 individual simulations, we find that the system is so unstable that the planets proposed simply cannot exist, due to mean lifetimes of less than a thousand years across the whole parameter space. We then present a detailed re-analysis of the observational data on HW Vir, deriving a new orbital solution that provides a very good fit to the observational data. Our new analysis yields a system with planets more widely spaced, and of lower mass, than that proposed in the discovery work, and yields a significantly greater (and more realistic) estimate of the uncertainty in the orbit of the outermost body. Despite this, a detailed dynamical analysis of this new solution similarly reveals that it also requires the planets to move on orbits that are simply not dynamically feasible. Our results imply that some mechanism other than the influence of planetary companions must be the principal cause of the observed eclipse timing variations for HW Vir. If the sys- tem does host exoplanets, they must move on orbits differing greatly from those previously proposed. Our results illustrate the critical importance of performing dynamical analyses as a part of the discovery process for multiple-planet exoplanetary systems.

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Blobrana


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Title: The quest for companions to post-common envelope binaries: III. A reexamination of HW Virginis
Authors: K. Beuermann, S. Dreizler, F. V. Hessman, J. Deller

We report new mid-eclipse times of the short-period sdB/dM binary HW Vir, which differ substantially from the times predicted by a previous model. The proposed orbits of the two planets in that model are found to be unstable. We present a new secularly stable solution, which involves two companions orbiting HW VIr with periods of 12.7 yr and 55 ±15 yr. For orbits coplanar with the binary, the inner companion is a giant planet with mass M_3 sin i_3 = 14 Jupiter masses and the outer one a brown dwarf or low-mass star with a mass of M_4 sin i_4 = 30-120 Jupiter masses. Using the mercury6 code, we find that such a system would be stable over more than 10^7 yr, in spite of the sizeable interaction. Our model fits the observed eclipse-time variations by the light-travel time effect alone, without invoking any additional process, thereby providing support for the planetary hypothesis of the eclipse-time variations in close binaries. The signature of non-Keplerian orbits may be visible in the data.

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Blobrana


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HW Virginis, abbreviated HW Vir, is an eclipsing binary system (of the Algol type) approximately 590 light-years away (based on the stellar properties and magnitudes: the Hipparcos trigonometric parallax measurement has too high an error value to be useful) in the constellation of Virgo. The system comprises an eclipsing B-type subdwarf star and red dwarf star. The two stars orbit each other every 0.116795 days
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