On the Period Change of the Contact Binary GW Cephei

Details On the Period Change of the Contact Binary GW Cephei On the Period Change of the Contact Binary GW Cephei

Jun 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010jass...27...89k&link_type=abstract

Journal of Astronomy and Space Sciences. Vol. 27, no. 2, p. 89-96

Astronomy and Astrophysics

Astronomy

Eclipsing Binaries, Gw Cephei, Period Change, Light-Time Effect, Mass Transfer

Scientific paper

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 0.23-0.26 M&sun;-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 × 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 × 10-8 M&sun;/yr which is compatible with other W UMa-type contact binaries.

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