High-resolution spectroscopy of the intermediate polar EX Hydrae. I. Kinematic study and Roche tomography

Abstract

EX Hya is one of the few double-lined eclipsing cataclysmic variables that allow an accurate measurement of the binary masses. We analyze orbital phase-resolved UVES/ VLT high resolution spectroscopic observations of EX Hya with the aims of deriving the binary masses and obtaining a tomographic image of the illuminated secondary star. We present a novel method for determining the binary parameters by directly fitting an emission model of the illuminated secondary star to the phase-resolved line profiles of NaI lambda 8183/ 8195 in absorption and emission and CaII lambda 8498 in emission. The fit to the NaI and CaII line profiles, combined with the published K1, yields a white-dwarf mass M1 = 0.790 +/- 0.026 Msun, a secondary mass M2 = 0.108 +/- 0.008 Msun, and a velocity amplitude of the secondary star K2 = 432.4 +/- 4.8 km s-1. The secondary is of spectral type dM5.5 +/- 0.5 and has an absolute K-band magnitude of MK = 8.8. Its Roche radius places it on or very close to the main sequence of low-mass stars. It differs from a main sequence star by its illuminated hemisphere that faces the white dwarf. The secondary star contributes only 5% to the observed spin-phase averaged flux at 7500 A, 7.5% at 8200 A, and 37% in the K-band. We present images of the secondary star in the light of the NaI doublet and the CaII emission line derived with a simplified version of Roche tomography. We have discovered narrow spectral lines from the secondary star in EX Hya that delineate its orbital motion and allow us to derive accurate masses of both components. The primary mass significantly exceeds recently published values. The secondary is a low-mass main sequence star that displays a rich emission line spectrum on its illuminated side, but lacks chromospheric emission on its dark side.

arXiv comment15 pages, 15 figures, accepted for publication in Astronomy & Astrophysics

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• The Spin Period of EX Hydrae
• A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate
• Barnes-Evans relations for dwarfs with an application to the determination of distances to cataclysmic variables
• Model Atmospheres for Irradiated Stars in pre-Cataclysmic Variables
• HST/STIS Spectroscopy of the Intermediate Polar EX Hydrae
• A spectroscopic search for faint secondaries in cataclysmic variables
• Multi-wavelength spectrophotometry of EX Hydrae
• Distortion of secondaries in semi-detached binaries and the cataclysmic variable period minimum
• The Radial Velocity and Mass of the White Dwarf of EX Hydrae Measured with Chandra
• Infrared spectroscopy of cataclysmic variables - II. Intermediate polars
• Irradiated atmospheres of accreting magnetic white dwarfs with an application to the polar AM Herculis
• Spectroscopic Observations of the Intermediate Polar EX Hydrae in Quiescence
• Simultaneous X-ray and Optical Observations of EX Hydrae
• X-ray Light Curves and Accretion Disk Structure of EX Hydrae

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• Hard X-ray view on intermediate polars in the Gaia era
• Nova Scorpius 1437 A.D. is now a dwarf nova, age-dated by its proper motion
• A Catalogue of Potential Post Common Envelope Binaries
• GK Per and EX Hya: Intermediate polars with small magnetospheres
• The eclipsing post-common envelope binary CSS21055: a white dwarf with a probable brown-dwarf companion
• Observational evidence for matter propagation in accretion flows
• Herschel Observations of Cataclysmic Variables
• Infrared Spectroscopic Observations of the Secondary Stars of Short Period Sub-Gap Cataclysmic Variables
• X-ray reflection from cold white dwarfs in magnetic cataclysmic variables
• Testing the cooling flow model in the intermediate polar EX Hydrae
• The Magnetospheric Boundary in Cataclysmic Variables
• Neglected X-ray discovered polars: II: The peculiar eclipsing binary HY Eridani
• On the area of accretion curtains from fast aperiodic time variability of the intermediate polar EX Hya
• The Fe Line Flux Ratio as a diagnostic of the maximum temperature and the white dwarf mass of Cataclysmic Variables
• A Radial Velocity Study of the Intermediate Polar EX Hydrae
• Photoionized features in the X-ray spectrum of EX Hydrae
• Neglected X-ray discovered polars: III. RX J0154.0-5947, RX J0600.5-2709, RX J0859.1+0537, RX J0953.1+1458, and RX J1002.2-1925
• Features of the Accretion in the EX Hydrae System: Results of Numerical Simulation
• Variability of the Spin Period of the White Dwarf in the Magnetic Cataclysmic Binary System EX Hya
• Classifying IGR J15038-6021 as a magnetic CV with a massive white dwarf
• J1832.4-1627, the first eclipsing stream-fed intermediate polar
• X-ray spectroscopy method of white dwarf mass determination in intermediate polars. External systematic uncertainties
• Current and secular accretion rates of EX Hydrae
• Cyclical period changes in cataclysmic variables: a statistical study