ORFEUS II and IUE Spectroscopy of EX Hydrae

Using five high-resolution (λ/∆λ ≈ 3000) FUV (λλ = 910–1210 Å) spectra acquired in 1996 December during the flight of the ORFEUS-SPAS II mission, 47 archival IUE short-wavelength UV (λλ = 1150–1950 Å) spectra, and archival EUVE deep survey photometry (λλ ≈ 70–200 Å), we present a detailed picture of the behavior of the magnetic cataclysmic variable EX Hydrae in the vacuum ultraviolet. Like HUT spectra of this source, these FUV and UV spectra reveal broad emission lines of He II, C II–IV, N III and V, O VI, Si III–IV, and Al III superposed on a continuum which is blue in the UV and nearly flat in the FUV. Like ORFEUS spectra of AM Her, the O VI λλ1032, 1038 doublet is resolved into broad (FWHM ≈ 2000 km s) and narrow (FWHM ≈ 200 km s) emission components. Consistent with its behavior in the optical, and hence consistent with the accretion curtain model of this source, the FUV and UV continuum flux densities, the FUV and UV broad emission line fluxes, and the radial velocity of the O VI broad emission component all vary on the spin phase of the white dwarf, with the maximum of the FUV and UV continuum and broad emission line flux light curves coincident with maximum blueshift of the broad O VI emission component. On the binary phase, the strong eclipse of the EUV flux by the bulge on the edge of the accretion disk is accompanied by narrow and relatively weak absorption components of the FUV emission lines and 30%–40% eclipses of all the UV emission lines except He II λ1640, while the UV continuum is largely unaffected. Furthermore, both the flux and radial velocity of the O VI narrow emission component vary with binary phase. The relative phasing of the FUV and UV continuum light curves and the FUV emission-line radial velocities implicate the accretion funnel as the source of the FUV and UV continuum and the O VI broad emission component, and the white dwarf as the source of the O VI narrow emission component. Various lines of evidence imply that the density of both the broadand narrow-line regions is n∼10 11 cm, but the O VI line ratios imply that the narrow-line region is optically thick while the broad-line region is more likely optically thin. Subject headings: binaries: close — stars: individual (EX Hydrae) — stars: magnetic fields — ultraviolet: stars — white dwarfs