Cataclysmic Variable EX Hydrae Research Articles

X‐Ray Light Curves and Accretion Disk Structure of EX Hydrae

We present X-ray light curves for the cataclysmic variable EX Hydrae obtained with the Chandra High Energy Transmission Grating Spectrometer and the Extreme Ultraviolet Explorer Deep Survey photometer. We confirm earlier results on the shape and amplitude of the binary light curve and discuss a new feature: the phase of the minimum in the binary light curve, associated with absorption by the bulge on the accretion disk, increases with wavelength. We discuss several scenarios that could account for this trend and conclude that, most likely, the ionization state of the bulge gas is not constant, but rather decreases with binary phase. We also conclude that photoionization of the bulge by radiation originating from the white dwarf is not the main source of ionization, but that it is heated by shocks originating from the interaction between the in-flowing material from the companion and the accretion disk. The findings in this paper provide a strong test for accretion disk models in close binary systems.

The Radial Velocity and Mass of the White Dwarf of EX Hydrae Measured withChandra

We present the first detection of orbital motion in the cataclysmic variable EX Hydrae based on X-ray data from Chandra. The large collecting area of the telescope and the high resolution of the HETG spectrometers allow for an unprecedented velocity accuracy of ~15 km s-1 in the X-ray wavelength regime. We find an emission line velocity amplitude of 58.2 ± 3.7 km s-1 and infer a white dwarf mass of 0.49 ± 0.13 M☉, in good agreement with previous studies using optical, ultraviolet, and far-ultraviolet data.

A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate

Using the HST Fine Guidance Sensor, we have measured a high precision astrometric parallax of the cataclysmic variable EX Hydrae, $\pi=15.50\,\pm\,0.29$ mas. From the wavelength-integrated accretion-induced energy flux, we derive a quiescent accretion luminosity for EX Hya of $L_{\rm acc} = (2.6\pm 0.6)\times 10^{32}\,$ erg s -1 . The quiescent accretion rate then is $\dot M_{\rm av}=(6.2\pm 1.5)\times 10^{-11}(M_1/0.5\,{M}_\odot)^{-1.61}\, {M}_{\odot}\,{\rm yr}^{-1}$. The time-averaged accretion rate, which includes a small correction for the rare outbursts, is 6% higher. We discuss the system parameters of EX Hya and deduce $M_1 = 0.4-0.7$ $M_{\odot}$, $M_2 = 0.07-0.10$ $M_{\odot}$, and $i = 76.0^\circ-77.6^\circ$, using recent radial velocity measurements of both components and restrictions imposed by other observational and theoretical constraints. We conclude that the secondary is undermassive, overluminous, and expanded over a ZAMS star of the same mass. Near the upper limit to M 1 , the accretion rate of the white dwarf coincides with that due to near-equilibrium angular momentum loss by gravitational radiation and angular momentum transfer from the orbit into the spin-up of the white dwarf. Near the lower mass limit, the correspondingly higher accretion rate requires that either an additional angular momentum loss process is acting besides gravitational radiation or that accretion occurs on a near-adiabatic time scale. The latter possibility would imply that EX Hya is in a transient phase of high mass transfer and the associated spin-up of the white dwarf.

ORFEUS IIandIUESpectroscopy of EX Hydrae

Using ORFEUS-SPAS II FUV spectra, IUE UV spectra, and archival EUVE deep survey photometry, we present a detailed picture of the behavior of the magnetic cataclysmic variable EX Hydrae. Like HUT spectra of this source, the 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 doublet is resolved into broad and narrow emission components. Consistent with its behavior in the optical, 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 broad dip in the EUV light curve is accompanied by strong eclipses of the UV emission lines and by variations in both the flux and radial velocity of the O VI narrow emission component. The available data are consistent with the accretion funnel being the source of the FUV and UV continuum and the O VI broad emission component, and the white dwarf being the source of the O VI narrow emission component.

Time-resolved spectrophotometry of the cataclysmic variable EX Hydrae

Resultats d'une etude basee sur 264 spectres optiques resolus dans le temps, pour cette nova naine a eclipses inhabituelles

A model for the X-ray emitting cataclysmic variable EX Hydrae

view Abstract Citations (37) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A model for the X-ray emitting cataclysmic variable EX Hye. Cowley, A. P. ; Hutchings, J. B. ; Crampton, D. Abstract A high-time-resolution spectroscopic study of EX Hya indicates that the broad emission lines originate in a large accretion disk surrounding a white dwarf of approximately 0.7 solar masses. An unseen companion of 0.16 solar masses briefly eclipses part of the disk during the 98-minute orbital period. No clear evidence for the 67-minute photometric period is found spectroscopically. Publication: The Astrophysical Journal Pub Date: June 1981 DOI: 10.1086/158948 Bibcode: 1981ApJ...246..489C Keywords: Eclipsing Binary Stars; Novae; Stellar Spectra; Variable Stars; White Dwarf Stars; X Ray Sources; Emission Spectra; Line Spectra; Orbital Mechanics; Spectral Line Width; Stellar Mass Accretion; Stellar Motions; Astrophysics full text sources ADS | data products SIMBAD (6)