An ultraviolet study of the semi-detached eclipsing binary star system TT Hydrae

TT Hydrae is an Algol-type interacting binary star consisting of a B9.5 V primary star and a K1 III-IV companion star. The companion star fills its Roche lobe and is transferring matter onto the primary star via a gas stream that flows through the binary system's first Lagrange point. The orbital period of the two stars is 6.95 days. This orbital period is long enough that the gas stream most likely does not strike the primary star directly, but gives it a glancing impact.; The model of the mass flow in the binary system being presented is one of a "river" of material flowing around the equator of the primary star at the level of its photosphere. This river of gas can be heated by accretional heating and friction with the photosphere to temperatures higher than the 10,000 K photospheric temperature of the primary star. Ultraviolet absorption lines of the high temperature ions Si IV (25,000 K) and C IV (35,000 K) are identified in the IUE absorption spectra at all orbital phases. This is consistent with the river model as the river encircles the primary star.; Another indication of the presence of the gas stream can be seen in the radial velocity curves of some spectral lines. When the radial velocities of the UV spectral lines are plotted versus orbital phase, some of them exhibit a deviation with respect to the orbital motion of the primary star. This deviation consists of excess positive radial velocity between orbital phases 0.6 and 0.9. The deviation has the correct sign and is within the correct orbital phase range to be consistent with the expected orientation of the gas stream.; Emission spectra were recorded during the total phase of primary eclipse. Spectra recorded by the Hubble Space Telescope show emission lines of C IV, Si IV, and N V. These lines exhibit high radial velocity magnitudes in the range of 300 km s-1 to 400 km s-1. Circular orbit velocities within a few solar radii of the primary star would have magnitudes this large. This is consistent with the presence of a hot corona-like structure located above the hot river along the equator of the primary star. No absorption lines of N V have been identified indicating the material containing the N V ions should be optically thin.; Spectra recorded by the FUSE spacecraft contain emission lines identified as being from O VI. They have radial velocity magnitudes between 40 km s-1 and 170 km s-1. These lines could be generated in the coronae of the primary star, the companion star, or in circumbinary material. No absorption lines of O VI have been identified in the far UV spectra recorded by the BEFS instrument indicating they should be formed in an optically thin medium.; An attempt was made to quantify the mass transfer rate by using difference spectra based on the IUE absorption spectra. Mass transfer values were calculated from twelve individual absorption lines. The method uses a first order approximation that is only valid for spectral lines which are optically thin. None of the analyzed lines meets this criterion so this value is a lower limit. The combined weighted value determined is on the order of -10-15 M⊙ yr-1. The uncertainties are large enough to make the value of the mass transfer rate indeterminate using this method and the available IUE data.