Reflection of the X-ray emission from the surface of the white dwarf should be present in all hard X-ray emitting CV systems. It is clearly identified in the Ginga 2… 20 keV spectra of the polars AM Her and EF Eri, and also in the quiescent spectra of the dwarf novae SS Cyg. The inclusion of the hard reflection spectrum lowers the derived continuum temperature, so resolving a long standing problem of the mismatch of the iron line and continuum properties, and, with more realistic multi-temperature continuua, the derived shock temperatures are close to those expected from theoretical models of a strong shock.

Variations in UBVRI are classified as: luminosity– and wavelength– dependent phase variations with differences from cycle-to-cycle; flares caused by accretion events; UV Cet-type flares from the secondary.

I present preliminary results from an analysis of the flickering in the only off-axis, high-state observation of AM Her with the ROSAT PSPC. At high Ṁ, the ROSAT count rates are dominated by optically-thick emission from the white-dwarf surface, which is heated directly by the accretion flow. This emission is very soft, predominantly below 0.4keV, and exhibits strong flickering.

We present preliminary results of an analysis of X-ray and optical data of the asynchronous AM Her star BY Cam [1]. We use X-ray data from EXOSAT (0.1… 50 keV), Ginga (1.5… 50 keV) and ROSAT (0.1…2.0 keV) and optical data obtained during a 45-day campaign in 1994.

There are 4 known periods: the orbital period (201.30 m), the spin period of the white dwarf (199.3303 m), a spin-orbit beat period (14.15 d) and a side-band period (197.4 m). The detection of this side-band period lends credence to the theory of [2], who suggest that for a stream accreting, diskless, magnetic CV a frequency, f = 2ωspin − Ωorb (=197.399 m), will appear as a strong spike in the power spectrum for certain systems. Wu & Mason (this volume) discuss a competing model where Pspin = 197.4 m.

Since its discovery, BY Cam was known to be an atypical AM Her type CV (Remillard et al. 1986). Observations showed the orbital and white-dwarf spin periods differ by about 1% (Silber et al. 1992). As the white dwarf rotates relative to the secondary, the accretion stream encounters different magnetic geometries, and hence follows different accretion paths to the white dwarf. The magnetic geometry seen by the accretion stream repeats at the beat period (1/Pbeat = 1/Pspin − 1/Porb), which is 7 to 20 d (the range is due to the uncertainty in the measured periods). The shape of the light curve changes from night to night, which can be explained by the changing geometry of the highly-beamed cyclotron emission. Even if the asynchronous rotation is the underlying cause of the changing light curve, the light curve could differ at similar beat phases if the threading process is chaotic. Previous attempts to study the beat period using IUE (Zucker et al. 1995) and optical data (Mason & Chanmugam 1992) have been inconclusive.

We present the analysis of BV photometry of BY Cam based on observations carried out in Crimea. The long QPOs in brightness were detected in both high and low brightness states. Their typical periods, equal to 6, 12 and 24 m, are found. The amplitude of the QPOs depends on the phase of Pbeat.

The long-term light curves of the AM Her type binary BY Cam and the nova-like variable PG 2133+115 are presented. The BVR observations were carried out at a 0.5 m telescope equipped with a high sensitive TV tube superisocon (Abramenko et al. 1978), the UBV photoelectric data were obtained at 0.6 and 1.25 m telescopes and the photographic estimates were made from the negatives obtained at the 0.4 m astrograph in Crimea.

Both stars show high and low brightness states. They show similar behaviour in some respects: the amplitude between high and low states was about two magnitudes in B, but the duration of a low state was approximately two months for BY Cam and 1… 2 years for PG 2133+115.

The emission from AM Her systems show a variety of time-variable phenomena, including flickering with a typical power spectrum slope of −1 to −2. The optical flickering is usually modeled as, or assumed to be, a shot noise process with many overlapping simultaneous shots. Panek (1980) found that, for AM Her, a consistent model could be constructed with randomly occurring 70… 90 s rectangular shots. The power spectrum had a v−2 shape above 0.02 Hz as expected, although it is not clear whether a break in the slope of the power spectrum was actually seen around 0.01 Hz. There are many additional reports in the literature of ‘characteristic time-scales’ on the order of tens of seconds. However we are not aware of any case where the reported time-scale has been supported by e.g. a break in the power density spectrum. It is easy to show that the usual method of estimating a ‘characteristic time-scale’ from the auto correlation function of de-trended data will suggest such a characteristic time-scale even if none is present in the original time series. The evidence for shot noise in AM Her light curves therefore needs a re-examination. In this paper we give a short summary of our analysis of optical flickering in V834 Cen, based on high speed photometry obtained at ESO in 1987. Details will be reported elsewhere.

We have used the High Speed Photometer (HSP) aboard the Hubble Space Telescope to observe the magnetic cataclysmic variables VV Pup, AM Her, and V834 Cen in the UV (1400…3300 Å) with 0.01 s time resolution. We detected low frequency flickering in all three systems, and compare the time-scales with the predictions of King (1989). At higher frequencies we searched for shock oscillations from the accretion column(s) in these systems. The data were analyzed using the Gabor transform wavelet-like technique (Heil & Walnut 1989) to search for frequency evolution throughout each observation. Preliminary analysis suggests the detection of rapid UV quasi-periodic oscillations (QPOs) in VV Pup at 0.74 Hz, and at 4.4 Hz in V834 Cen. As in ground based observations, our observations failed to yield any rapid QPOs in AM Her itself.

We report on the Hubble Space Telescope (HST) observation of the polar, QS Tel, made during 1994 June. Orbital modulation is present in both the continuum and lines. A narrow dip is observed in the continuum folded light curve. The spectrum of the occulted source during this dip is broadly consistent in shape with the Rayleigh-Jeans tail of the EUV source.

With simultaneous blue (λλ4200–5000 Å) and far-red (λλ7950–8380 Å) phase-resolved, high resolution spectrophotometry, we re-examine the magnetic CV QQ Vul. A thorough radial velocity and flux analysis of all the observable features is carried out. We derive a complete set of system parameters and classify the donor star to be a spectral type M4.5 V. In addition to the Balmer, He I and He II emission lines in the blue range, arising from the accretion regions, we detect various emission features which solely follow the movement of the secondary star. The lines, which we interpret as reprocessed light from the illuminated hemisphere of the donor star, are Mg II at λ4481 Å, He II at λ8236 Å and C I at λ8335 Å. Intensity maps based on the line flux and radial velocity variations of the Na I absorption near λ8190 Å and Mg II emission feature were also made. These show that the line distribution on the surface of the donor is consistent with being symmetric. As a result of our analysis the position of the real zero phase was found to be at ϕ = 0.42 of the linear polarisation ephemeris.

We present X-ray and optical observations of the ROSAT discovered polar (AM Her binary) RX J1015.5+0904 and first results of our analysis of the X-ray and optical data. These results indicate a one-pole accretion geometry and an orbital period of P = 79.88 m for this V ~ 17 mag system.

Observations with the Hopkins Ultraviolet Telescope on the Astro-1 and Astro-2 space shuttle missions have provided the first set of moderate (3 Å) resolution far ultraviolet (FUV) spectra of dwarf novae to include the wavelength range between Lyα and the Lyman limit. Important lines which are detected in the HUT spectra of dwarf novae in this wavelength range include S VI λλ933,945, C III λ977, O VI λλ1032,1038, P V λλ1118,1128 and C III λ1176, as well as the higher order Lyman lines. The observations confirm earlier IUE observations that two dwarf novae – U Gem and VW Hyi – have quiescent FUV spectra dominated by the white dwarf, but suggest that the quiescent FUV emission from three other dwarf novae – SS Cyg, WX Hyi and YZ Cnc – are dominated by emission from a hot portion of the disk or a disk corona. The spectra obtained of the dwarf novae Z Cam and EM Cyg in outburst and also of the nova-like variable IX Vel can be modeled reasonably successfully in terms of steady state disks constructed by adding appropriately-weighted stellar model spectra.

EUVE observed the SU UMa-type dwarf nova VW Hyi in superoutburst for an interval of nearly 2 d in 1994 June and produced EUV light curves and the first EUV spectrum of this important CV.

We have re-analyzed UV spectra of the dwarf nova VW Hyi during its quiescence, obtained with the Faint Object Spectrograph (FOS) on Hubble Space Telescope (HST), by considering the possible contribution from the accretion disk, which was not included in the previous analysis.

We present a preliminary analysis of the UV spectrum of the dwarf nova VW Hyi during early quiescence, obtained with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST). The data were obtained approximately one day after the end of a normal outburst.

We estimate the post-outburst cooling time-scale of the white dwarf in VW Hyi, using the available quiescent IUE spectra. The determination of the white-dwarf temperature close to the outburst is hampered because disc emission still contributes to the SWP flux.

We present preliminary results of a modelling campaign based on HST eclipse observations of the wind-formed C IV resonance line in the eclipsing nova-like variable UX UMa. Within the framework of a simple kinematic accretion disk wind model, we are currently able to reproduce the shapes (but not the strengths) of the observed line profiles away from and during eclipse, as well as the behaviour of the integrated line flux light curve. The most important aspect of our modelling is that it suggests the presence of a vertically extended, relatively dense and slow moving transition region between the disk photosphere and the fast wind.

Los Alamos National Laboratory’s ALEXIS satellite, containing six wide field of view EUV telescopes was launched 1993 April 25. ALEXIS is a sky monitor/survey experiment, and with each 50 s rotation, the satellite’s six telescopes (three energy bands 130, 178 and 186 Å) scan nearly half of the sky. Due to the damage sustained at launch by the satellite, the ALEXIS project team has had to spend over a year devising new methods to determine spacecraft attitude knowledge, essential for putting photons back on the sky correctly. These efforts have been successful. A recent review of the ALEXIS point source effort can be found in the Proceedings of IAU Colloquium 152, 1995. This paper reviews the transient systems that have been observed by ALEXIS which fall into two types: cataclysmic variables and unknown, short duration transients.

ASCA has observed ~20 cataclysmic variables since launch. In this review, we present the current status of ASCA observations of CVs and scientific results. In Sect. 2, we introduce the scientific instruments of ASCA, and show the list of CVs observed so far. Data analysis and results on magnetic and non-magnetic CVs are described in Sect. 3 and 4, respectively. In Sect. 5, we make a brief summary.