A new photometric study of the triple star system EF Draconis  

作　　者：Yuan-Gui Yang 

机构地区：[1]School of Physics and Electronic Information,Huaibei Normal University,Huaibei 235000,China [2]Key Laboratory of the Structure and Evolution of Celestial Objects,Chinese Academy of Sciences,Kunming 650011,China

出　　处：《Research in Astronomy and Astrophysics》2012年第4期419-432,共14页天文和天体物理学研究（英文版）

基　　金：supported by the National Natural Science Foundation of China (Nos.10778707 and 11133007);Anhui Provincial Natural Science Foundation (No.1208085MA04);the Open Research Program (No.OP 201110) of the Key Laboratory for the Structure and Evolution of Celestial Objects of CAS

摘　　要：We present new charge-coupled device （CCD） photometry for the triple star EF Draconis, obtained in 2009 and 2011. Using the updated Wilson-Devinney program, the photometric solutions were deduced from two sets of light curves. The results indicate that EF Dra is an A-type W UMa binary with a contact degree of f = 46.7%（ ± 0.6%） and a third light of l 3 ■1.5%. Through analyzing the O C curve, it is found that the orbital period shows a long-time increase with a lighttime orbit. The period, semi-amplitude and eccentricity of the third body are P mod = 17.20（ ± 0.18） yr, A = 0.0039 d （ ± 0.0002 d ） and e = 0.49（ ± 0.02） respectively. This kind of tertiary companion may extract angular momentum from the central system. The orbital period of EF Dra secularly increases at a rate of dP/dt = ＋3.72（ ± 0.07） × 10 7 d yr 1 , which may be interpreted by mass transfer from the less massive to the more massive component. As period increases, the separation between components may increase, which will cause the contact degree to decrease. With mass transferring, the spin angular momentum will increase, while the orbital angular momentum will decrease. Only if the contact configuration would merge at J spin 〉1/3 J orb could this kind of deep-contact binary with period increasing, such as EF Dra, evolve into a rapidly-rotating single star.We present new charge-coupled device （CCD） photometry for the triple star EF Draconis, obtained in 2009 and 2011. Using the updated Wilson-Devinney program, the photometric solutions were deduced from two sets of light curves. The results indicate that EF Dra is an A-type W UMa binary with a contact degree of f = 46.7%（ ± 0.6%） and a third light of l 3 ■1.5%. Through analyzing the O C curve, it is found that the orbital period shows a long-time increase with a lighttime orbit. The period, semi-amplitude and eccentricity of the third body are P mod = 17.20（ ± 0.18） yr, A = 0.0039 d （ ± 0.0002 d ） and e = 0.49（ ± 0.02） respectively. This kind of tertiary companion may extract angular momentum from the central system. The orbital period of EF Dra secularly increases at a rate of dP/dt = ＋3.72（ ± 0.07） × 10 7 d yr 1 , which may be interpreted by mass transfer from the less massive to the more massive component. As period increases, the separation between components may increase, which will cause the contact degree to decrease. With mass transferring, the spin angular momentum will increase, while the orbital angular momentum will decrease. Only if the contact configuration would merge at J spin 〉1/3 J orb could this kind of deep-contact binary with period increasing, such as EF Dra, evolve into a rapidly-rotating single star.

关 键 词：stars （including multiple）： binaries： close — stars： individual （EF Draconis） 

分 类 号：P144[天文地球—天体物理]