HST/STIS Spectroscopy of the Intermediate Polar EX Hydrae

TL;DR

This study uses high-resolution HST/STIS spectroscopy to analyze the UV properties of the intermediate polar EX Hydrae, revealing details about its emission sources, white dwarf mass, and accretion disk characteristics.

Contribution

It provides detailed spectral modeling and precise measurements of the white dwarf and accretion disk properties in EX Hydrae, enhancing understanding of intermediate polars.

Findings

White dwarf mass estimated at 0.91 M_sun

Emission line fluxes modulated more than continuum flux

Accretion disk truncated at 2.5 R_WD

Abstract

We present the results of our analysis of six orbits of 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+/-0.05 M_sun. 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 0.9 M_sun, T=23000 K, an accretion disk truncated at 2.5 R_WD, and is at a distance of 60 pc.