1999MNRAS.305..966B

The relatively bright eclipsing RS CVn binary CF Tuc was observed in both optical (photometry and spectroscopy) and microwave ranges in a `multisite, multiwavelength' campaign in 1996.

The microwave data, gathered using the Australia Telescope Compact Array, covered slightly more than one complete orbital cycle at 4.8 and 8.64 GHz in one continuous run. There was also limited coverage at 1.38 and 2.38 GHz. High-dispersion spectroscopy was obtained using the McLellan 1-m telescope and echelle spectrograph at Mt John University Observatory (New Zealand). Supporting photometry came from smaller scale facilities associated with the Royal Astronomical Society of New Zealand (RASNZ).

The data show the correlation between microwave signal enhancement and photometric flux diminution (maculation effect) noted previously in similar studies. The spectroscopy also points to the phenomena being related to a very enhanced active region on the secondary star located close to the maculation region.

Cross-correlation of the microwave emission data between the 4.8- and 8.64-GHz ranges shows a strong positive correlation, with a significant lag of the 4.8-GHz behind the 8.64-GHz variations. This indicates energized waves propagating through the corona of the K4 subgiant at the electron sound speed. The emitting region may have been eclipsed by the primary star, but such eclipse effects are of marginal significance for the present analysis.

An attempt is made to put all the evidence into one coherent picture of the active region.