Orbital period modulation and spot activity in the RS?CVn binary V711?Tauri

摘要

Aims. We attempt to establish the real nature of the orbitalperiod variation and its relation to the spot activity ofV711Tau, and determine why the (B-V)colour of the star appears to be nearly independent of its Vmagnitude.We wish to verify whether existing predictions in the literature forthe long-term spot activity of the star are true or not by makingextended photometric observations, and whether the broad component of Hemissionoriginates in more localised active regions, assuggested by somechromospheric models, bysearching for any correlation between thebase-line width of the emission and the light modulation. Methods. We obtained new radial velocities of the G-type component of V711Tau on 42 nights during 2004-09, and BVphotometryof V711Tau on 202nights during the years1993-2009. Wemeasured the equivalent widths of two well resolved lines of the G-typecomponent from13 of the spectra obtained byus. We alsomeasured the equivalent widths and base-line widths of Hemissionfrom 21spectra obtained during 2008-09. We analyse these alongwith relevant information available in the literature. Results. The available radial velocity data of V711 Tauare consistent with a sinusoidal modulation of its orbital period; theperiod of modulation is found to be 36.31.9yr. The fractional light-loss over a photometric cycle is found to vary with an average period of 14.10.3yr. Itappears that physical processes linked to themagnetic activity of the spotted star are responsible for the variationin the orbital period. The excess reduction in the Bband flux relative to that in Vbandcaused by spot activity is almost compensated for by the fractionalincrease in the contribution by the hotter companion to the total lightin the blue spectral region, and thereby makes the (B-V)colour of the binary system nearly independent of its Vmagnitude. We find that the ratio of the radii of the components derived from their vsinivalues,which is usually quoted in the literature, issubstantially largerthan that implied by the ratio of their brightnesses in Vband. There is a slight indication from the Vbanddata that the spot activity in V711Tau has a component that isfixed in the orbital frame of reference. The equivalent width andbase-line width of Hemission do not show any obvious correlation with the Vband light curve. Key words: stars: activity - binaries: spectroscopic - stars: individual: V711Tau- stars: late-type - starspots