CCD PHOTOMETRY OF CONTACT BINARY WZ Cephei

Lee, Woo-Baik; Kang, Yun Hee; Oh, Kyu-Dong

doi:10.5140/jass.2008.25.1.019

Cited by 1 publication

(9 citation statements)

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“…Their analysis of both their own light curves and Hoffmann's using their own Roche computer model (Djurašević 1992a, b) showed that the WZ Cep system is a shallow contact binary (f = 9~14%) with the components of slightly different temperatures (ΔT ≈ 140 K) and with two large dark spots on the surface of the massive, hotter primary star. Recently, WZ Cep was revisited by Lee et al (2008) and Zhu & Qian (2009). Lee et al (2008) presented symmetrical BVR light curves in the observing season in 2005, while Zhu & Qian (2009) obtained an asymmetrical V light curve with a strong O'Connell effect.…”

Section: Period Studymentioning

confidence: 99%

“…Recently, WZ Cep was revisited by Lee et al (2008) and Zhu & Qian (2009). Lee et al (2008) presented symmetrical BVR light curves in the observing season in 2005, while Zhu & Qian (2009) obtained an asymmetrical V light curve with a strong O'Connell effect. Both authors analyzed their light curves using the WD method and confirmed the photometric results of Djurašević et al (1998).…”

Section: Period Studymentioning

confidence: 99%

“…GSC 4486-1402 and GSC 4486-1352 were chosen as the comparison and check stars, respectively. Our comparison is the same one used by Lee et al (2008). http://janss.kr although there is a large gap of about 25 years between 1939 y and 1964 y .…”

Section: Observationsmentioning

confidence: 99%

“…In principle, there are two working mechanisms for the secular period decrease observed in a close binary star such as the WZ Cep system: 1) secular mass transfer from the more massive ("primary" hereinafter) to the less massive ("secondary" hereinafter) stars, 2) angular momentum loss (AML) by magnetic braking via a magnetically controlled stellar wind from a magnetically active star in a binary. WZ Cep has been known as a shallow contact system with a fill-out factor of about 9-24% (Djurašević et al 1998, Lee et al 2008, Zhu & Qian 2009 and with the massive primary hotter than the secondary. Moreover, the primary star has a large and variable dark spot(s) (Djurašević et al 1998, Lee et al 2008, Zhu & Qian 2009, indicating that it is a magnetically active star.…”

Section: The Secular Period Decreasementioning

confidence: 99%

“…WZ Cep has been known as a shallow contact system with a fill-out factor of about 9-24% (Djurašević et al 1998, Lee et al 2008, Zhu & Qian 2009 and with the massive primary hotter than the secondary. Moreover, the primary star has a large and variable dark spot(s) (Djurašević et al 1998, Lee et al 2008, Zhu & Qian 2009, indicating that it is a magnetically active star. This would mean that both a secular transfer of a gaseous mass stream from the primary to the secondary star and the AML from the magnetically active primary star are occurring concurrently in the WZ Cep system.…”

Section: The Secular Period Decreasementioning

confidence: 99%

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WZ Cephei: A Dynamically Active W UMa-Type Binary Star

Jeong¹,

Kim²

2011

Journal of Astronomy and Space Sciences

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An intensive analysis of 185 timings of WZ Cep, including our new three timings, was made to understand the dynamical picture of this active W UMa-type binary. It was found that the orbital period of the system has complexly varied in two cyclical components superposed on a secularly downward parabola over about 80 y . The downward parabola, corresponding to a secular period decrease of -9. d 97 × 10 -8 y -1 , is most probably produced by the action of both angular momentum loss (AML) due to magnetic braking and mass-transfer from the massive primary component to the secondary. The period decrease rate of -6. d 72 × 10 -8 y -1 due to AML contributes about 67% to the observed period decrease. The mass flow of about 5.16 × 10 -8 M ⊙ y -1 from the primary to the secondary results the remaining 33% period decrease. Two cyclical components have an 11. y 8 period with amplitude of 0. d 0054 and a 41. y 3 period with amplitude of 0. d 0178. It is very interesting that there seems to be exactly in a commensurable 7:2 relation between their mean motions. As the possible causes, two rival interpretations (i.e., light-time effects (LTE) by additional bodies and the Applegate model) were considered. In the LTE interpretation, the minimum masses of 0.30 M ⊙ for the shorter period and 0.49 M ⊙ for the longer one were calculated. Their contributions to the total light were at most within 2%, if they were assumed to be main-sequence stars. If the LTE explanation is true for the WZ Cep system, the 7:2 relation found between their mean motions would be interpreted as a stable 7:2 orbit resonance produced by a long-term gravitational interaction between two tertiary bodies. In the Applegate model interpretation, the deduced model parameters indicate that the mechanism could work only in the primary star for both of the two period modulations, but could not in the secondary. However, we couldn't find any meaningful relation between the light variation and the period variability from the historical light curve data. At present, we prefer the interpretation of the mechanical perturbation from the third and fourth stars as the possible cause of two cycling period changes.

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