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Aims. Emission lines in polars show complex profiles with multiple components that are typically ascribed to the accretion stream, threading region, accretion spot, and the irradiated secondary-star. In low-state polars the fractional contribution by the accretion stream, and the accretion spot is greatly reduced offering an opportunity to study the effect of the secondary-star irradiation or stellar activity. We observed VV Pup during an exceptional low-state to study and constrain the properties of the line-forming regions and to search for evidence of chromospheric activity and/or irradiation.

Aims.We investigated the low state of the polar VV Pup by collecting high S/N time series spectra.

We report the detection of a 110 MG cyclotron harmonic in the SDSS-spectrum of the magnetic cataclysmic variable (MCV) RX J1554.2+2721. This feature was noted earlier by others but remained unexplained. The wide spectral coverage of the new spectrum together with the earlier detection of a Zeeman split Lyαline in a field of 144 MG makes the identification almost unambiguous. We propose to explain the non-conforming UV-optical photospheric temperature of the white dwarf by an as yet unobserved cyclotron component in the ultraviolet which also could significantly contribute to the overall energy balance of the accretion process.

We have examined the radial velocity data for stars spectroscopically observed by the Sloan Digital Sky Survey (SDSS) more than once to investigate the incidence of spectroscopic binaries, and to evaluate the accuracy of the SDSS stellar radial velocities. We find agreement between the fraction of stars with significant velocity variations and the expected fraction of binary stars in the halo and thick disk populations. The observations produce a list of 675 possible new spectroscopic binary stars and orbits for eight of them.

We present the results of a campaign of simultaneous observations of V603 Aql in the X-ray and UV bands accomplished with the IUE and ROSAT satellites. Simultaneous observations cover 20 orbital cycles, while the total span of all the observations is 40 cycles. This constitutes the longest continuous UV time series of simultaneous space observations of a cataclysmic variable. As all high energy radiation is ultimately powered by accretion, it is perhaps remarkable that we observe some signs of correlations of the UV line and continuum emission with the X-ray flux at zero lag, but none over a range of time lags from $400{-}40\,000 ~\mbox{s}$. A hint of some lagged correlation was revealed for UV color and X-ray flux. We detect a very strong modulation of intensity of the UV lines of CIV and SiIV. The modulation appears coherent over the range of observation and its period of $0.1380(5) ~{\rm d}$is consistent with the spectroscopic orbital period but differs significantly from the period of photometric modulation. Furthermore, we observe variable P-Cygni profiles of the CIV1550 line. Its absorption and emission components are modulated with the orbital period of the binary. These data present evidence for sustained asymmetry of the supersonic wind excited from the accretion disc yet pose difficulties for the current disc and wind models. Since no periodic modulation was found in the X-ray band nor in the UV continuum, the present data do not lend support to our earlier classification of V603 Aql as an intermediate polar.

We report on the first far-UV observations of the asynchronous polar BY Cam made by the Far-Ultraviolet Spectroscopic Explorer (FUSE). The source is known to exhibit the most extreme NV/CIV emission resonance line ratio observed among polars. The FUSE observations reveal a OVI resonance line weaker than in the prototype of polars, AM Her, with the absence of a detectable narrow component. The OVI broad line is detected with an equivalent width of the same order as in AM Her, the blueward doublet component is clearly present but the redward component is strongly affected by H2absorption. The presence of a strong NIII line and weak CIII lines also confirms the peculiar CNO line flux. We compare the resonance CNO line intensities with the predictions of the CLOUDY plasma code coupled to a geometrical model of the accretion column. Varying the temperature and/or intensity of the ionising spectrum is unable to reproduce the observed broad line ratios. A solution is obtained by significantly altering the element abundances with a strong depletion of C, overabundance of N and a weak underabundance of O. This confirms previous suggestions of non-solar abundances which may result from redistribution in the accreted material following nova outbursts and/or the secondary nuclear evolution. A very significant H2absorption is observed in front of the source, a possible indication for either the existence of a dense interstellar cloud or of circumstellar material.

We present multi-color photometry and time resolved spectroscopy of OU Vir. The analysis of the quiescent light curve shows that OU Vir is characterized by i) strong cycle-to-cycle brightness variations, and ii) hot spot modulated light curve with grazing eclipse of the impact region. Colors are derived both in- and out- of eclipse. The time-resolved spectroscopy allows us to produce the radial velocity curve from the Hαaccretion disk emission line which possibly reveals only weak evidence for hot spot line emission. The hot spot is believed to be a turbulent optically thick region, producing mostly continuum emission.

We report here on the identification and study of the optical counterpart of the ROSAT source RX J0704.2+6203. Extensive spectral and photometric observation showed that the object belongs to the class of magnetic Cataclysmic Variables. We determined the orbital period of the system to be 97$.\!\!^{\rm m}$27 and estimated the strength of its magnetic field to be on the order of 20 MG. The system was observed in both high and low states, common for its class. Other parameters of the magnetic close binary system were estimated. The spectral and photometric behavior of the object is similar to that of the well studied polar BL Hyi.

We present high resolution Hubble Space Telescope ultraviolet spectroscopy of the dwarf nova EK TrA obtained in deep quiescence. The Space Telescope Imaging Spectrograph data reveal the broad ${\rm Ly\alpha}$absorption profile typical of a moderately cool white dwarf, overlayed by numerous broad emission lines of He, C, N, and Si and by a number of narrow absorption lines, mainly of CIand SiII. Assuming a white dwarf mass in the range 0.3-1.4 $M_{\odot}$we derive $T_{\rm eff}=17 500$-$23 400$K for the primary in EK TrA; $T_{\rm eff}=18 800$K for a canonical mass of 0.6 $M_{\odot}$. From the narrow photospheric absorption lines, we measure the white dwarf rotational velocity, $v\sin i=200\pm100$$\rm km s^{-1}$. Even though the strong contamination of the photospheric white dwarf absorption spectrum by the emission lines prevents a detailed quantitative analysis of the chemical abundances of the atmosphere, the available data suggest slightly sub-solar abundances. The high time resolution of the STIS data allows us to associate the observed ultraviolet flickering with the emission lines, possibly originating in a hot optically thin corona above the cold accretion disk.