Journal of Astronomy and Space Sciences

The Korean Space Science Society (한국우주과학회)
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On the Period Change of the Contact Binary GW Cephei

  • Kim, Chun-Hwey (Department of Astronomy and Space Science, Chungbuk National University) ;
  • Song, Mi-Hwa (Department of Astronomy and Space Science, Chungbuk National University) ;
  • Yoon, Joh-Na (Chungbuk National University Observatory, Chungbuk National University) ;
  • Jeong, Jang-Hae (Department of Astronomy and Space Science, Chungbuk National University) ;
  • Jeoung, Taek-Soo (Department of Astronomy and Space Science, Chungbuk National University) ;
  • Kim, Young-Jae (Department of Astronomy and Space Science, Chungbuk National University) ;
  • Kim, Jung-Yeb (Department of Astronomy and Space Science, Chungbuk National University)
  • Received : 2010.04.24
  • Accepted : 2010.05.06
  • Published : 2010.06.15
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Abstract

BVR CCD observations of GW Cep were made on 15 nights in November through December 2008 with a 1-m reflector at the Jincheon station of the Chungbuk National University Observatory. Nineteen new times of minimum lights for GW Cep were determined and added to a collection of all other times of minima available to us. These data were then intensively analyzed, by reference to an O-C diagram, to deduce the general form of period variation for GW Cep. It was found that the O-C diagram could be interpreted as presenting two different forms of period change: an exclusively quasi-sinusoidal change with a period of 32.6 years and an eccentricity of 0.10; and a quasi-sinusoidal change with a period of 46.2 years and an eccentricity of 0.36 superposed on an upward parabola. Although a final conclusion is somewhat premature at present, the latter seems more plausible because late-type contact binaries allow an inter-exchange of both energy and mass between the component stars. The quasi-sinusoidal characteristics were interpreted in terms of a light-time effect due to an unseen tertiary component. The minimum masses of the tertiary component for both cases were calculated to be nearly the same as the $0.23-0.26M\;{\odot}$-ranges which is hardly detectable in a light curve synthesis. The upward parabolic O-C diagram corresponding to a secular period increase of about $4.12{\times}10^{-8}\;d/yr$ was interpreted as mass being transferred from the lesser to more massive component. The transfer rate for a conservative case was calculated to be about $2.66\;{\times}\;10^{-8}\;M_{\odot}/yr$ which is compatible with other W UMa-type contact binaries.

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