The Extreme Ultraviolet Explorer ( EUVE ) satellite was employed for 5.46 days beginning on 1999 February 9.03 UT to acquire phase-resolved EUV photometric and spectroscopic observations of the AM Her-type cataclysmic variable V834 Centauri .
The resulting data are superior to those obtained by EUVE beginning on 1993 May 28.14 UT because the source was approximately three times brighter , the observation was four times longer and dithered , and ASCA observed the source simultaneously .
Although we do not understand the EUV light curves in detail , they are explained qualitatively by a simple model of accretion from a ballistic stream along the field lines of a tilted ( [ \beta, \psi ] \approx [ 10 ^ { \circ } , 40 ^ { \circ } ] ) magnetic dipole centered on the white dwarf .
In 1993 when the EUV flux was lower , accretion was primarily along the \varphi \approx \psi \approx 40 ^ { \circ } field line , whereas in 1999 when the EUV flux was higher , accretion took place over a broad range of azimuths extending from \varphi \approx \psi \approx 40 ^ { \circ } to \varphi \approx 76 ^ { \circ } .
These changes in the accretion geometry could be caused by an increase in the mass-accretion rate and/or the clumpiness of the flow .
The 75–140 Å EUVE spectra are well described by either a blackbody or a pure-H stellar atmosphere absorbed by a neutral hydrogen column density , but constraints on the size of the EUV emission region and its UV brightness favor the blackbody interpretation .
The mean 1999 EUV spectrum is best fit by an absorbed blackbody with temperature kT \approx 17.6 eV , hydrogen column density N _ { H } \approx 7.4 \times 10 ^ { 19 } ~ { } cm ^ { -2 } , fractional emitting area f \approx 10 ^ { -3 } , 70–140 Å flux \approx 3.0 \times 10 ^ { -11 } ~ { } erg~ { } cm ^ { -2 } ~ { } s ^ { -1 } , and luminosity L _ { soft } \approx 7.2 \times 10 ^ { 32 } ( d / 100 ~ { } { pc } ) ^ { 2 } ~ { } erg~ { } s ^ { -1 } .
The ratio of the EUV to X-ray luminosities is L _ { soft } / L _ { hard } \approx 40 , signaling that some mechanism other than irradiation ( e.g. , blob heating ) dominates energy input into the accretion spot .
The 1999 SW hardness ratio variation can be explained by minor variations in kT and/or N _ { H } , but instead of tracking the SW count rate variation , the hardness ratio variation was sinusoidal , with a minimum ( maximum ) when the accretion spot was on the near ( far ) side of the white dwarf , consistent with the trend expected for an atmosphere with an inverted temperature distribution .