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Title:
ORFEUS II and IUE Spectroscopy of EX Hydrae
Authors:
Mauche, Christopher W.
Publication:
The Astrophysical Journal, Volume 520, Issue 2, pp. 822-832. (ApJ Homepage)
Publication Date:
08/1999
Origin:
APJ
ApJ Keywords:
STARS: BINARIES: CLOSE, STARS: INDIVIDUAL (EX HYDRAE), STARS: MAGNETIC FIELDS, ULTRAVIOLET: STARS, STARS: WHITE DWARFS
DOI:
10.1086/307498
Bibliographic Code:
1999ApJ...520..822M

Abstract

Using five high-resolution (lambda/Deltalambda~3000) FUV (910-1210 Å) spectra acquired in 1996 December during the flight of the ORFEUS-SPAS II mission, 47 archival IUE short-wavelength UV (1150-1950 Å) spectra, and archival EUVE deep survey photometry (70-200 Å), we present a detailed picture of the behavior of the magnetic cataclysmic variable EX Hydrae in the vacuum ultraviolet. Like Hopkins Ultraviolet Telescope spectra of this source, these far-ultraviolet (FUV) and UV spectra reveal broad emission lines of He II, C II-CIV, N III and N V, O VI, Si III-S IV, and Al III superposed on a continuum that is blue in the UV and nearly flat in the FUV. Like ORFEUS spectra of AM Her, the O VI lambdalambda1032, 1038 doublet is resolved into broad (FWHM~2000 km s^-1) and narrow (FWHM~200 km s^-1) 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 lambda1640, while the UV continuum is largely unaffected. Furthermore, both the flux and radial velocities 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 implicate the white dwarf as the source of the O VI narrow emission component. Various lines of evidence imply that the density of both the broad- and narrow-line regions is n>~10^11 cm^-3, 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.
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