Open AccessPhotometric investigation of three W UMa‐type binary stars in the old open cluster NGC 188
Author(s) -
Liu L.,
Qian S.B.,
Zhu L.Y.,
He J.J.,
Liao W.P.,
Li L.J.,
Zhao E.G.,
Wang J.J.
Publication year - 2011
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2011.18914.x
Subject(s) - physics , open cluster , astrophysics , orbital period , stars , cluster (spacecraft) , light curve , radius , star cluster , astronomy , oscillation (cell signaling) , computer security , biology , computer science , genetics , programming language
In a programme to understand the evolution of contact binaries, we have re‐observed EQ Cep, ER Cep and V371 Cep, which are members of the old open cluster NGC 188, photometrically. Combining our photometric solutions with some known parameters of the cluster, we derived the mass and the radius for each component. Meanwhile, we investigated the period changes of the three systems, finding a long‐term increase of period in every system and discovering two cyclic variations in ER Cep besides the long‐term changes ( T 3 = 5.40 ± 0.01 yr, A 3 = 0.0135 ± 0.0016 d; T 4 = 17.6 ± 0.1 yr). From the derived physical parameters and analysis of the orbital period, we conclude that (i) both components of V371 Cep have very possibly evolved off the main sequence, as a result of the derived accelerations of gravity log g 1 = 3.93 and log g 2 = 3.98 , and (ii) ER Cep is at least a triple, or even quadruple, system, something suggested by the overmassive derived total mass ( ∼3.51 M ⊙ ) and the 5.4‐yr‐cycle periodic oscillation.