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We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variables AC Cnc and V363 Aur (= Lanning 10). There is evidence of irradiation on the inner hemisphere of the secondary star in both systems, which we correct for using a model that reproduces the observations remarkably well. We find the radial velocity of the secondary star in AC Cnc to be KR = 176 ± 3 km s-1 and its rotational velocity to be v sin i = 135 ± 3 km s-1. From these parameters we obtain masses of M1 = 0.76 ± 0.03 M⊙ for the whitedwarf primary and M2 = 0.77 ± 0.05 M⊙ for the K2 ± 1V secondary star, giving a mass ratio of q = 1.02 ± 0.04. We measure the radial and rotational velocities of the G7 ± 2V secondary star in V363 Aur to be KR = 168 ± 5 km s-1 and v sin i = 143 ± 5 km s-1, respectively. The component masses of V363 Aur are M1 = 0.90 ± 0.06 M⊙ and M2 = 1.06 ± 0.11 M⊙, giving a mass ratio of q = 1.17 ± 0.07. The mass ratios for AC Cnc and V363 Aur fall within the theoretical limits for dynamically and thermally stable mass transfer. Both systems are similar to the SW Sex stars, exhibiting single-peaked emission lines with transient absorption features, high-velocity S-wave components and phase-offsets in their radial-velocity curves. The Balmer lines in V363 Aur show a rapid increase in flux around phase 0 followed by a rapid decrease, which we attribute to the eclipse of an optically thick region at the centre of the disc. This model could also account for the behaviour of other SW Sex stars where the Balmer lines show only a shallow eclipse compared to the continuum. [ABSTRACT FROM AUTHOR]

We present polarimetric and spectroscopic observations of the ROSAT source RX J1313.32-3259, recently identified as a polar. Circular polarization is modulated over the orbital period with an amplitude of ∼10 per cent. A brief reversal in circular polarization is detected at phase ∼0.0, when the main accretion region is seen face on to the observer. We deduce that the main cyclotron emission is absorbed by the accretion shock and/or stream at this phase, allowing a second accretion shock, located at the opposite ends of the field lines that feed the main pole, to be seen. Linear polarization is also detected with possible linear pulses at orbital phases where the accretion region is expected to be on the limb of the white dwarf. The general morphology of the photopolarimetry arises as a result of a combination of the absorption of cyclotron radiation by the accretion shock/stream and projection/cyclotron beaming effects of a main cyclotron emission region as the white dwarf rotates. The main cyclotron emission region remains on the visible hemisphere of the white dwarf throughout the orbit. Doppler maps of the emission lines show emission at or near the expected location of the secondary star and an extended arc-like feature coincident with the ballistic and possibly the magnetically confined accretion stream. [ABSTRACT FROM AUTHOR]

We present spectroscopic and high-speed photometric data of the eclipsing polar V895 Cen. We find that the eclipsed component is consistent with it being the accretion regions on the white dwarf. This is in contrast to Stobie et al. who concluded that the eclipsed component was not the white dwarf. Further, we find no evidence for an accretion disc in our data. From our Doppler tomography results, we find that the white dwarf has M≳0.7 M[sub ⊙]. Our indirect imaging of the accretion stream suggests that the stream is brightest close to the white dwarf. When we observed V895 Cen in its highest accretion state, emission was concentrated along field lines leading to the upper pole. There is no evidence for enhanced emission at the magnetic coupling region. [ABSTRACT FROM AUTHOR]

We report observations that confirm the identities of the optical counterparts to the transient sources RX J0544.1–7100 and RX J0520.5–6932. The counterparts are suggested to be B-type stars. Optical data from the observations carried out at ESO and SAAO, together with results from the OGLE data base, are presented. In addition, X-ray data from the RXTE All-Sky Monitor are investigated for long-term periodicities. A strong suggestion for a binary period of 24.4 d is seen in RX J0520.5–6932 from the OGLE data. [ABSTRACT FROM AUTHOR]

Multiwavelength monitoring observations of the AM Her system, QS Tel, are presented, the centrepiece being a coordinated campaign with the ASCA, EUVE and HST satellites and optical observations on 1996 September 28–29. The star was initially observed in an intermediate brightness, single pole state in 1996 April by ROSAT. However two EUVE snapshots of the system in August found it in a deep low state, the light curves appearing to retain a bright and faint phase morphology although the bright interval showed significant phase drifts compared with the earlier ROSAT data. At this time, the system appeared optically bright, while polarimetry pointed to one active pole. A modest recovery of intensity, albeit accompanied by an apparently chaotic extreme ultraviolet (EUV) light curve, was subsequently recorded during the coordinated run in late September. This brightening was confirmed by a second ROSAT pointing in early October, although the EUV brightening is matched by a marked decay in its optical output. These observations, all of which found the system in a fainter EUV state than seen in 1993, add to the catalogue of accretion mode behaviour in QS Tel. However, as yet, the data base of observations does not allow us to establish whether the accretion mode is dictated by accretion-rate dependent penetration of the magnetosphere or asynchronous rotation. The ASCA spectrum obtained during the coordinated observation is adequately described by a thermal spectrum with a temperature of about 4.4 keV and an absorbing column density of less than 8×10[sup 20] cm[sup -2]. At the same time, the 1150–2600 Å UV HST spectrum shows a strong, broad Lyα absorption profile which we attribute to the white dwarf. We infer an effective temperature of 16 000–19 000 K and a mass between 0.5 and 0.93 M[sub ⊙] for the white dwarf, at least some of the uncertainty arising because the profile is very probably contaminated and broadened by Zeeman features. The orbital variation seen by HST can be matched by a blackbody-like spectrum with a temperature above 24 000 K. The near UV part of the spectrum contains evidence of phase-variable cyclotron harmonics. [ABSTRACT FROM AUTHOR]

Focuses on the X-ray source in the Small Magellanic Cloud (SMC) from the ROSAT Positions Sensitive Proportional Counter archive. Luminosity of SMC; Identification of the source as an X-ray pulsar; Estimation of the absolute magnitude of the SMC system.

We present polarimetric and spectroscopic observations of the ROSAT source RX J1141.3-6410, recently identified as a polar. The detection of circular polarization variations, with an amplitude of 10 per cent, over a 3.16-h period confirms that the system is a polar (AM Herculis star). Supporting evidence comes from the nature of the emission lines and their radial velocity variability. In addition, we observe continuum slope changes in the far-red spectral region (∼6000–8200 Å), indicative of phase dependent cyclotron emission. Polarimetric modelling at two wavelengths establishes RX J1141.3-6410 as a single-pole system, with i∼β∼70°. The accretion region is extended in magnetic longitude, and is totally self-occulted for ∼25 per cent of the orbit. The radial velocity curves derived from the emission lines show a phasing with maximum blueshift occurring with Δφ∼0.05 of maximum intensity and circular polarisation. In addition, the broader component of the lines exhibit a substantial radial velocity phase shift with respect to the narrower component, in the sense that the broad component preceeds the narrow. This can be readily understood if the narrower component is principally a result of orbital motion of the stream material and the broad component mainly a result of streaming motion near the coupling region. The phasing of the Ca ii near-infrared line radial velocities also supports this general picture. [ABSTRACT FROM AUTHOR]

We present simultaneous optical polarimetry and X-ray data of the near-synchronous polar RX J2115–5840. We model the polarization data using the Stokes imaging technique of Potter et al. We find that the data are best modelled using a relatively high binary inclination and a small angle between the magnetic and spin axes. We find that, for all spin–orbit beat phases, a significant proportion of the accretion flow is directed on to the lower hemisphere of the white dwarf, producing negative circular polarization. Only for a small fraction of the beat cycle is a proportion of the flow directed on to the upper hemisphere. However, the accretion flow never occurs near the upper magnetic pole, whatever the orientation of the magnetic poles. This indicates the presence of a non-dipole field with the field strength at the upper pole significantly higher. We find that the brightest parts of the hard X-ray emitting region and the cyclotron region are closely coincident. [ABSTRACT FROM AUTHOR]

We present a detailed mode identification performed on the 1994 Whole Earth Telescope (WET) run on GD 358. The results are compared with that obtained for the same star from the 1990 WET data. The two temporal spectra show very few qualitative differences, although amplitude changes are seen in most modes, including the disappearance of the mode identified as k=14 in the 1990 data. The excellent coverage and signal-to-noise ratio obtained during the 1994 run lead to the secure identification of combination frequencies up to fourth order, i.e. peaks that are sums or differences of up to four parent frequencies, including a virtually complete set of second-order frequencies, as expected from harmonic distortion. We show how the third-order frequencies are expected to affect the triplet structure of the normal modes by back-interacting with them. Finally, a search for ℓ=2 modes was unsuccessful, not verifying the suspicion that such modes had been uncovered in the 1990 data set. [ABSTRACT FROM AUTHOR]

We present a small sample of time-resolved optical spectroscopy of the dwarf nova HL CMa during an outburst state. By combining radial velocity measurements with published data we show that the previously quoted value is not the only candidate for the orbital period of this system. We reduce the significance of daily aliasing but cannot distinguish between two periods at 0.2146±0.0004 and 0.2212±0.0005 d. We show that the low-excitation emission lines are composites from an accretion disc and the companion star, and that high-excitation emission originates in the disc or outflowing material associated with the accreting white dwarf. [ABSTRACT FROM AUTHOR]

The fields of eight X-ray sources in the Magellanic Clouds believed to be Be/X-ray binaries have been searched for possible Be-star counterparts. BVR[sub c] and Hα CCD imaging was employed to identify early-type emission stars through colour indices and Hα fluxes. Spectroscopy of five sources confirms the presence of Hα emission in each case. Based on the positional coincidence of emission-line objects with the X-ray sources, we identify Be-star counterparts to the ROSAT sources RX J0032.9-7348, RX J0049.1-7250, RX J0054.9-7226 and RX J0101.0-7206, and to the recently discovered ASCA source AX J0051-722. We confirm the Be star nature of the counterpart to the HEAO1 source H0544-66. In the field of the ROSAT source RX J0051.8-7231 we find that there are three possible counterparts, each showing evidence for Hα emission. We find a close double in the error circle of the EXOSAT source EXO 0531.1-6609, each component of which could be a Be star associated with the X-ray source. [ABSTRACT FROM AUTHOR]

CP Tuc (AX J2315–592) shows a dip in X-rays which lasts for approximately half the binary orbit and is deeper in soft X-rays compared with hard X-rays. It has been proposed that this dip is due to the accretion stream obscuring the accretion region from view. If CP Tuc were a polar, as has been suggested, then the length of such a dip would make it unique amongst polars since in those polars in which a dip is seen in hard X-rays the dip lasts for only 0.1 of the orbit. We present optical polarimetry and RXTE observations of CP Tuc which show circular polarization levels of ∼10 per cent and find evidence for only one photometric period. These data confirm CP Tuc as a polar. Our modelling of the polarization data implies that the X-ray dip is due to the bulk of the primary accretion region being self-eclipsed by the white dwarf. The energy dependence of the dip is due to a combination of this self-eclipse and also the presence of an X-ray temperature gradient over the primary accretion region. [ABSTRACT FROM AUTHOR]