On the RZ Draconis substellar circumbinary companions: stability study of the proposed substellar circumbinary system

Hinse, Tobias C. and Horner, Jonathan and Lee, Jae Woo and Wittenmyer, Robert A. and Lee, Chung-Uk and Park, Jang-Ho and Marshall, Jonathan P. (2014) On the RZ Draconis substellar circumbinary companions: stability study of the proposed substellar circumbinary system. Astronomy and Astrophysics, 565. A104. ISSN 0004-6361

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Context. Recently, using the light-travel time effect, planets and substellar companions have been proposed to orbit around binary star systems (also known as circumbinary companions) as a result of variations in timing of the observed eclipses. For the majority of these systems the proposed orbital architecture features a crossing of the orbital configurations as a result of high eccentricities for one or both of the companions. For such systems, strong mutual gravitational interactions are expected, resulting in catastrophic orbital instabilities, or collisions between the proposed components, on very short timescales.
Aims. We re-examine the primary and secondary eclipse timings of the short-period and semi-detached binary RZ Draconis (RZ Dra). The proposed companions were reported to have masses of around ≃ 0.07 and ≃ 0.18 M⊙ with the inner companion on an orbit with moderate eccentricity (0.46), whose apocenter distance crosses the orbit of the outer companion. We show that the companions proposed previously follow highly unstable orbits. In an attempt to find a stable system we searched the underlying χ2 parameter space for a best-fit model and carried out an orbit-stability study to test possible best-fit models. If the binary period changes are truly due to additional massive companions in a hierarchical configuration, they must follow stable orbits.
Methods. For numerical orbital stability calculations we used well established orbit integration routines. Computations were carried out using a large-scale multi-CPU computing environment. Our data analysis of times of primary and secondary eclipse is based on the Levenberg-Marquardt least-squares minimization algorithm using the two-body Keplerian light-travel time effect model.
Results. Despite the wide variety of potential models tested for the RZ Dra system in this work, we found very few models that were stable for even one million years, with the vast majority of systems tested falling apart on timescales of just hundreds of years. It seems therefore likely that the observed timing variations are not solely the result of massive, unseen companions.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: © 2014 ESO. This publication is copyright. It may be reproduced in whole or in part for the purposes of study, research, or review, but is subject to the inclusion of an acknowledgment of the source.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - No Department
Date Deposited: 25 Jun 2014 06:32
Last Modified: 08 Mar 2017 05:18
Uncontrolled Keywords: binaries; eclipsing; celestial mechanics; numerical methods: observational; stars formation; RZ Draconis
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020103 Cosmology and Extragalactic Astronomy
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020105 General Relativity and Gravitational Waves
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1051/0004-6361/201423799
URI: http://eprints.usq.edu.au/id/eprint/25357

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