ABSTRA C T We systematically searched the non-proprietary data in the Hubble Space Telescope (HST) Archive to identify low-redshift quasars that have been imaged with the Wide Field Planetary Camera-2 (WFPC-2) but that have not yet been presented in the literature. We identified five such objects. Since these represent a significant increment to the number of WFPC-2 imaged quasars previously presented in the literature, we here present images of these objects and a discussion of their properties. Of the five objects, two are involved in spectacular ongoing gravitational interactions. This brings the total number of quasars seen on WFPC-2 images to be in such interactions to 11. A further two of the five quasars have close companion objects (i.e. within 30 kpc) suggestive of a recent interaction. No evidence for an interaction can be seen on the fifth quasar. All five host systems are brighter than L, in keeping with the results found for other quasars imaged with WFPC-2. Three of the five quasars are at least 2.5 mag brighter than L, and are among the brightest host galaxies imaged with WFPC-2. The results widen the derived difference in the mean absolute luminosity of the hosts of radio-quiet quasars compared with the hosts of radio-loud quasars.

Quasar host galaxy images from the Hubble Space Telescope Archive

We present phase-resolved, high-resolution (1.3 A) spectroscopy of the brightest near-synchronous polar BY Cam taken on two different occasions in 1998 and 1999. The first tomographic study of such a system reveals line emission spread out over a large velocity range forming a crescent at negative vy velocities in the Doppler maps. In contrast to the majority of synchronous AM Her systems there is only weak indication for the presence of a focused accretion stream. These two facts suggest that the majority of the matter is accreted via an extended curtain. Location and extent of the structure in the Doppler maps can be reproduced with a simple curtain model raised over a wide (∼180 ◦ ) range in azimuth implying that the ballistic stream stretches to a point far behind the white dwarf. In order to reach such small magnetospheric radii mass accretion rates a factor of 10 to 20 in excess of that normally seen in polars would be required. In addition to the curtain emission, the Balmer lines show a narrow emission line component likely originating from the heated side of the secondary star. Its velocity amplitude of

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Doppler tomography of the asynchronous polar BY Camelopardalis

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 ob- served 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 aected by H2 absorption. 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 col- umn. 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 H 2 absorption is observed in front of the source, a possible indication for either the existence of a dense interstellar cloud or of circumstellar material.

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The surprising Far-UV spectrum of the polar BY Camelopardalis

The X-Ray Timing Explorer

Analysis of 15 yr of photometric monitoring of the asynchronous magnetic cataclysmic variable BY Cam leads to revised assignments of the periodicities in the system. The surprising stability of the 197.4-min period suggests that this is the orbital period. We confirm the 7.3-d beat period between the orbital period and the white dwarf spin period, and show that the observed periods of the orbit, spin and beat are consistent to within the errors. In earlier work, the 197.4-min period has been assigned to the 2ω - Ω sideband. Because of the observed stability of the 197.4-min period in our data, the synchronization time of BY Cam is >3500 yr (much larger than that in other asynchronous polars) if the earlier period assignments are adopted. We also suggest that ∼145-d periodicity seen in our data may be due to precession of the rotational pole of the white dwarf.

Long-term photometry of the asynchronous polar BY Cam: a period study

The discovery of an AM Herculis-type magnetic variable, an accreting binary system that contains a magnetic white dwarf and a late-type companion, is reported. The proposed optical counterpart to the detected X-ray source exhibits all the optical emission characteristics of its class: circular polarization, strongly modulated brightness variations, intense flickering on time scales of seconds, historical 'low states', and intense emission lines, including very strong lines of He II. The modulations in the polarization and the photometric magnitude suggest an orbital period of 3.1 + or -0.2 hr.

J. Patterson

Papers

H0538 + 608 - A bright AM Herculis-type X-ray source