  New high-resolution spectra, of the chromospherically active binary system CF
Tuc, taken at the Mt. John University Observatory in 2007, were analyzed 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: $a_{1}{\sin}i$=$0.0254\pm0.0001$ AU,
$a_{2}{\sin}i$=$0.0228\pm0.0001$ AU, $M_{1}{\sin}i$=$0.902\pm0.005$
$M_{\odot}$, and $M_{2}{\sin}i$=$1.008\pm0.006$ $M_{\odot}$. 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:
$M_{1}$=$1.11\pm0.01$ $M_{\odot}$, $M_{2}$=$1.23\pm0.01$ $M_{\odot}$,
$R_{1}$=$1.63\pm0.02$ $R_{\odot}$, $R_{2}$=$3.60\pm0.02$ $R_{\odot}$,
$L_{1}$=$3.32\pm0.51$ $L_{\odot}$ and $L_{2}$=$3.91\pm0.84$ $L_{\odot}$. 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 $89\pm6$ pc from the dynamic parallax, neglecting
interstellar absorption, in agreement with the Hipparcos value.
