The close T Tauri binary V 4046 Sagittarii

We have collected high-resolution (R approximate to 60 000) VLT-UVES spectrograms of the close T Tauri binary V 4046 Sgr from 3500-6750 Angstrom at different phases of its 2.4 day orbital period. The high quality of these spectra allows us to present an improved ephemeris of the system. To model the photospheric absorption line spectrum we calculate synthetic spectra for the observed phases of the system. These synthetic spectra are used to determine veiling levels, and to extract emission line profiles that are undistorted by photospheric absorption lines. We find that the shapes of the strong emission lines of H and Ca II H & K all vary periodically with phase. A weak veiling continuum is superimposed on the stellar absorption line spectra. The Ca II H & K emission lines are composed of two narrow emission components that closely follow the stellar orbital motion, and we speculate that these lines are formed in global chromospheric networks on the stars. Also the Balmer lines have similar narrow stellar components, possibly also chromospheric. However, in addition there are extended wings on each side of the line centers of all H lines, which change dramatically in shape with the orbital phase. We find that the shape and velocity changes of the wing components are consistent with two concentrations of gas moving at high velocity but co-rotating with the stars. These concentrations move with a projected velocity of 80 km s(-1) around the center of mass. They are located well inside the edge of the circumbinary disk, and also inside the co-linear Lagrangian points of this binary. With this concept we obtain a very good agreement between calculated and observed line profiles of H8, H9 and H 10 as a function of phase. In some recent calculations of mass transfer from circumbinary disks to close binaries in circular motion, accumulations of gas in co-rotation with the stars develop, resulting in structures which are similar to what we have found from Our observations. We also investigate the cause of periodic photometric variations observed by others.