The chromospherically--active binary CF Tuc revisited

Abstract

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: $a_1\sin i$=$0.0254\pm 0.0001$ AU, $a_2\sin i$=$0.0228\pm 0.0001$ AU, $M_1\sin i$=$0.902\pm 0.005$ $M_{\odot }$, and $M_2\sin i$=$1.008\pm 0.006$ $M_{\odot }$. 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: $M_1$=$1.11\pm 0.01$ $M_{\odot }$, $M_2$=$1.23\pm 0.01$ $M_{\odot }$, $R_1$=$1.63\pm 0.02$ $R_{\odot }$, $R_2$=$3.60\pm 0.02$ $R_{\odot }$, $L_1$=$3.32\pm 0.51$ $L_{\odot }$ and $L_2$=$3.91\pm 0.84$ $L_{\odot }$. 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 $89\pm 6$ pc from the dynamic parallax, neglecting interstellar absorption, in agreement with the Hipparcos value.

33 pages, 10 figures, accepted for publication by MNRAS

References in corpus (5)

• Validation of the new Hipparcos reduction
• Basic physical parameters of a selected sample of evolved stars
• A catalog of chromospherically active binary stars (third edition)
• Spots, plages, and flares on lambda Andromedae and II Pegasi
• Combining astrometry with the light-time effect: The case of VW Cep, zeta Phe and HT Vir

Cited by in corpus (1)

• Orbital and physical parameters of eclipsing binaries from the ASAS catalogue -- IX. Spotted pairs with red giants