By using all available times of light minimum, the orbital period changes of a W UMa eclipsing binary YY CrB have been investigated. Two possible orbital period variations are found: (1) a secular period decrease with a rate of dP/dt = −6.727 × 10−7 d yr−1, on which a sinusoidal oscillation with a period of P = 12.68 yr is superposed, or (2) an abrupt period change with a sudden period decrease of −0.7862 s around the year 2005. The secular period decrease is discussed in terms of (1) the mass transfer from the more massive companion to the less massive one with a mass transfer rate of dM2/dt = 2.8096 × 10−7 M⊙ yr−1, and (2) the mass loss via stellar wind from the system. The sinusoidal oscillatory can be interpreted as a result of the magnetic activity cycles of the system. In addition, the abrupt period decrease of the system might be due to the sudden mass transfer between the components.
We present a study of orbital period changes in AH Virginis. We perform a careful literature search for all available minima times, from which we derived a new linear ephemeris and constructed an O — C curve. We found that the orbital period of AH Virginis shows a long-term increase, dP/dt = (2.1869 ± 0.0161) × 10−7 d yr−1, and a small periodic variation with a period of 37.19 yr. Since AH Virginis is an over-contact system and the primary component shows strong Hα and Mg II emission lines, we discuss the possible connection between mass transfer, magnetic activity and orbital period changes.
In this paper, we present new CCD photometric observations of AH Tauri in the R band observed in 2006 at the Yunnan Observatory. Two new times of light minima were derived from these observations. We modeled the light curves using the 2003 version of the Wilson-Devinney program. The results show that the variations of the light curves can be expained by a cool spot on the primary star. The fill-out factor is about 6.6%, indicating that AH Tauri is a shallow-contact system. The mass ratio was determined to be about 0.505. In addition, the orbital period variations of AH Tauri were investigated based on all of the photoelectric and CCD light minimum times, including our two new data. It was found that the orbital period exhibits a possible periodic variation with a period of P 54.62 ( 0.20) mod = years and a secular period decrease of dP dt (1.823 0.215) 10 days yr 7 1= -´--. Since AH Tauri is an overcontact solar-like system, we discuss three mechanisms of the mass transfer, the lighttime effect of the third body, and magnetic activity responsible for the orbital period changes.
The light curves of RT CrB in the B and V bands observed by İbanoğlu et al. (1985, Ap&SS, 112, 133), and in the V band and the radial velocity curves observed by Sabby and Lacy (2003, AJ, 125, 1448), are analyzed using the Wilson–Devinney code. The results show that the distortions in the light curve observed by Sabby and Lacy (2003) can be fitted by two spots, a hot spot on the primary component and a cool spot on the secondary star. The temperature ratios of the spotted region to the photosphere, Ts/Tph, are 1.181(±0.053) and 0.803(±0.057) respectively. Combining the radial velocity curves with the light curves, our analysis gives reliable, accurate estimates of the physical parameters of the system, M1 = 1.35(±0.01)M⊙ and R1 = 2.88(±0.05)R⊙ for the primary (hotter) component, M2 = 1.36(±0.01)M⊙ and R2 = 2.92(±0.04)R⊙ for the secondary (cooler) component. In addition, the orbital period variations of RT CrB are investigated based on all available times of light minima collected from literature and databases. We find that the orbital period exhibits a possible long-term period decrease with a rate of dP/dt = −3.11 × 10−7 d yr−1, suggesting that RT CrB is undergoing an angular momentum loss via magnetic braking.
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