Hubble Space Telescope Space Telescope Imaging Spectrograph Spectroscopy of the Intermediate Polar EX Hydrae

Abstract

We present the results of our analysis of six orbits of Hubble Space Telescope Space Telescope Imaging Spectrograph (HST/STIS) time-tagged spectroscopy of the intermediate polar, EX Hydrae. The high time and wavelength resolution of the HST/STIS spectra provided an excellent opportunity to study the UV properties of EX Hya. Measurements of the continuum and emission-line fluxes corroborate earlier studies that show that the emission-line fluxes are modulated more strongly than the continuum flux and originate from the accretion curtains, while the continuum flux originates from the white dwarf photosphere. The measured K amplitude of the narrow emission-line radial velocity curve is used to calculate a white dwarf mass of 0.91+/-0.05M_solar. Synthetic white dwarf photosphere and accretion disk spectral models are used to further refine the white dwarf and accretion disk properties. Using the spectral models, it is determined that EX Hya has a white dwarf of mass 0.9M_solar, T=23,000 K, and an accretion disk truncated at 2.5R_WD and is at a distance of 60 pc.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposal 8807.