* Astronomy

Title: The chromospherically--active binary CF Tuc revisited
Authors: D. Dogru, A. Erdem, S. S. Dogru, S. Zola

New high-resolution spectra, of the chromospherically active binary system CF Tuc, 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: a_{1}{\sin}i=0.0254±0.0001 AU, a_{2}{\sin}i=0.0228±0.0001 AU, M_{1}{\sin}i=0.902±0.005 M_{\odot}, and M_{2}{\sin}i=1.008±0.006 M_{\odot}. The cooler component of the system shows H\alpha and CaII H & K emissions. 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: M_{1}=1.11±0.01 M_{\odot}, M_{2}=1.23±0.01 M_{\odot}, R_{1}=1.63±0.02 R_{\odot}, R_{2}=3.60±0.02 R_{\odot}, L_{1}=3.32±0.51 L_{\odot} and L_{2}=3.91±0.84 L_{\odot}. 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 massive third body (possibly a black hole) in the system. The distance to CF Tuc was calculated to be 89±6 pc from the dynamic parallax, neglecting interstellar absorption, in agreement with the Hipparcos value.

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Position(2000): RA 00 53 07.7668, Dec -74 39 05.621