The Algol System SZ Herculis: Physical Nature and Orbital Behavior

TL;DR

This study analyzes the physical and orbital characteristics of the Algol-type binary SZ Her, revealing period variations likely caused by two M-type companions, and provides detailed photometric and orbital analysis.

Contribution

It presents the first comprehensive photometric and orbital analysis of SZ Her, identifying two potential M-type companions influencing its orbital period.

Findings

The system is a classical Algol-type binary with specific physical parameters.

Orbital period variations suggest two M-type companions causing light-time effects.

The companions are near a 2:1 mean motion resonance.

Abstract

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$^\circ$.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 behavior 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 M$_\odot$ and $M_4$=0.19 M$_\odot$, 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.