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Post Info TOPIC: SZ Herculis
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SZ Herculis
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Title: The Proposed Quadruple System SZ Herculis: Revised LITE Model and Orbital Stability Study
Authors: T. C. Hinse, K. Gozdziewski, J. W. Lee, N. Haghighipour, C.-U. Lee

In a recent study, Lee et al. presented new photometric follow-up timing observations of the semi-detached binary system SZ Herculis and proposed the existence of two hierarchical cirumbinary companions. Based on the light-travel time effect, the two low-mass M-dwarf companions are found to orbit the binary pair on moderate to high eccentric orbits. The derived periods of these two companions are close to a 2:1 mean-motion orbital resonance. We have studied the stability of the system using the osculating orbital elements as presented by Lee et al. Results indicate an orbit-crossing architecture exhibiting short-term dynamical instabilities leading to the escape of one of the proposed companions. We have examined the system's underlying model parameter-space by following a Monte Carlo approach and found an improved fit to the timing data. A study of the stability of our best-fitting orbits also indicates that the proposed system is generally unstable. If the observed anomalous timing variations of the binary period is due to additional circumbinary companions, then the resulting system should exhibit a long-term stable orbital configuration much different from the orbits suggested by Lee et al. We, therefore, suggest that based on Newtonian-dynamical considerations, the proposed quadruple system cannot exist. To uncover the true nature of the observed period variations of this system, we recommend future photometric follow-up observations that could further constrain eclipse-timing variations and/or refine light-travel time models.

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Title: The Algol System SZ Herculis: Physical Nature and Orbital Behaviour
Authors: Jae Woo Lee, Chung-Uk Lee, Seung-Lee Kim, Ho-Il Kim, Jang-Ho Park

Multiband CCD photometric observations of SZ Her were obtained between 2008 February and May. The light curve was completely covered and indicated a significant temperature difference between both components. The light-curve synthesis presented in this paper indicates that the eclipsing binary is a classical Algol-type system with parameters of q=0.472, i=87.57°, and \Delta(T_{1}--T_{2})=2,381 K; the primary component fills approximately 77% of its limiting lobe and is slightly larger than the lobe-filling secondary. More than 1,100 times of minimum light spanning more than one century were used to study an orbital behaviour of the binary system. It was found that the orbital period of SZ Her has varied due to a combination of two periodic variations with cycle lengths of P_3=85.8 yr and P_4=42.5 yr and semi-amplitudes of K_3=0.013 d and K_4=0.007 d, respectively. The most reasonable explanation for them is a pair of light-time effects (LITEs) driven by the possible existence of two M-type companions with minimum masses of M_3=0.22 solar masses and M_4=0.19 solar masses, that are located close to the 2:1 mean motion resonance. If two additional bodies exist, then the overall dynamics of the multiple system may provide a significant clue to the formation and evolution of the eclipsing pair.

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