A dynamical analysis of the proposed circumbinary HW Virginis planetary system
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2012 RAS © 2012 The Authors.Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved ; In 2009, the discovery of two planets orbiting the evolved binary star system HW Virginis (HW Vir) 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 thiswork, we perform a highly detailed analysis of the proposedHWVir 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 system 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 ; We also thankDr Lee JaeWoo for useful discussions and suggestions that resulted in the creation of Fig. 2. JH gratefully acknowledges the financial support of the Australian government through ARC Grant DP0774000. RAW is supported by a UNSW Vice-Chancellor's Fellowship. JPM is partly supported by Spanish grants AYA 2008/01727 and AYA 2011/02622. TCH gratefully acknowledges financial support from the Korea Research Council for Fundamental Science and Technology (KRCF) through theYoung Research Scientist Fellowship Program, and also the support of the Korea Astronomy and Space Science Institute (KASI) grant 2012-1-410-02. The dynamical simulations performed in this work were performed on the EPIC supercomputer, supported by iVEC, located at theMurdoch University, in Western Australia. The Monte Carlo/fitting simulations were carried out on the 'Beehive' computing cluster at Armagh Observatory (UK) and the 'Pluto' high performance computing cluster at the KASI. Astronomical research at Armagh Observatory (UK) is funded by the Department of Culture, Arts and Leisure