2009MNRAS.397.1647D

This paper presents results derived from analysis of new spectroscopic and photometric observations of the chromospherically active binary system CF Tuc. New high-resolution spectra, taken at the Mt. John University Observatory in 2007, were analysed using two methods: cross-correlation and Fourier-based disentangling. As a result, new radial velocity curves of both components were obtained. The resulting orbital elements of CF Tuc are a₁sini = 0.0254±0.0001au, a₂sini = 0.0228±0.0001au, M₁sini = 0.902±0.005M_☉ and M₂sini = 1.008±0.006M_☉. The cooler component of the system shows Hα and Caii H&K emissions. Using simultaneous spectroscopic and photometric observations, an anticorrelation between the Hα emission and the BV light curve maculation effects was found. This behaviour indicates a close spatial association between photospheric and chromospheric active regions. Our spectroscopic data and recent BV light curves were solved simultaneously using the Wilson-Devinney code. A dark spot on the surface of the cooler component was assumed to explain large asymmetries observed in the light curves. The following absolute parameters of the components were determined: M₁= 1.11±0.01M_☉, M₂= 1.23±0.01M_☉, R₁= 1.63±0.02R_☉, R₂ = 3.60±0.02R_☉, L₁= 3.32±0.51L_☉ and L₂= 3.91±0.84L_☉. The primary component has an age of about 5Gyr and is approaching its main-sequence terminal age. The distance to CF Tuc was calculated to be 89±6pc from the dynamic parallax, neglecting interstellar absorption, in agreement with the Hipparcos value. The orbital period of the system was studied using the O-C analysis. The O-C diagram could be interpreted in terms of either two abrupt changes or a quasi-sinusoidal form superimposed on a downward parabola. These variations are discussed by reference to the combined effect of mass transfer and mass loss, the Applegate mechanism and also a light-time effect due to the existence of a third body in the system.