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We report extensive 3-yr multiwavelength observations of the WZ Sge-type dwarf nova SSS J122221.7-311525 during its unusual double superoutburst, the following decline and in quiescence. The second segment of the superoutburst had a long duration of 33 d and a very gentle decline with a rate of 0.02 mag d-1, and it displayed an extended post-outburst decline lasting at least 500 d. Simultaneously with the start of the rapid fading from the superoutburst plateau, the system showed the appearance of a strong near-infrared excess resulting in very red colours, which reached extreme values (B - I ≃ 1.4) about 20 d later. The colours then became bluer again, but it took at least 250 d to acquire a stable level. Superhumps were clearly visible in the light curve from our very first time-resolved observations until at least 420 d after the rapid fading from the superoutburst. The spectroscopic and photometric data revealed an orbital period of 109.80 min and a fractional superhump period excess ≲ 0.8 per cent, indicating a very low mass ratio q ≲ 0.045. With such a small mass ratio the donor mass should be below the hydrogen-burning minimum mass limit. The observed infrared flux in quiescence is indeed much lower than is expected from a cataclysmic variable with a near-main-sequence donor star. This strongly suggests a brown-dwarf-like nature for the donor and that SSS J122221.7-311525 has already evolved away from the period minimum towards longer periods, with the donor now extremely dim. [ABSTRACT FROM AUTHOR]

ABSTRACT We present an analysis of time-resolved, medium-resolution optical spectroscopic observations of UX Ursae Majoris (UX UMa) in the blue (3920-5250 Å) and red (6100-7200 Å) wavelength ranges that were obtained in 1999 April and 2008 March, respectively. The observed characteristics of our spectra indicate that UX UMa has been in different states during those observations. The blue spectra are very complex. They are dominated by strong and broad single-peaked emission lines of hydrogen. The high-excitation lines of He ii λ4686 and the Bowen blend are quite strong as well. All the lines consist of a mixture of absorption and emission components. Using Doppler tomography, we have identified four distinct components of the system: the accretion disc, the secondary star, the bright spot from the gas stream/disc impact region and the unique compact area of absorption in the accretion disc seen as a dark spot in the lower left-hand quadrant of the tomograms. In the red wavelength range, both the hydrogen (Hα) and neutral helium (He i λ6678 and He i λ7065) lines were observed in emission and both exhibited double-peaked profiles. Doppler tomography of these lines reveals spiral structure in the accretion disc, but in contrast to the blue wavelength range, there is no evidence for either the dark spot or the gas stream/disc impact region emission, while the emission from the secondary star is weak. During the observations in 1999, UX UMa showed many of the defining properties of the SW Sextantis stars. However, all these features almost completely disappeared in 2008. We have also estimated the radial velocity semi-amplitudes K1 and K2 and evaluated the system parameters of UX UMa. These estimates are inconsistent with previous values derived by means of analysis of white dwarf eclipse features in the light curve in different wavelength ranges. [ABSTRACT FROM AUTHOR]

PSR J0205+6449 is an X-ray and radio pulsar in supernova (SN) remnant 3C 58. We report on observations of the central region of 3C 58 using the 4.2-m William Herschel Telescope at the Isaac Newton Group of Telescopes, La Palma, with the intention of identifying the optical counterpart of PSR J0205+6449 and characterizing its pulsar wind nebula (PWN). Around the pulsar position, we identified extended emission with a magnitude of , and consistent with a PWN. From the R-band image, we identified three knots with (o1), 24.15 ± 0.07 mag (o2) and 24.24 ± 0.08 mag (o3). We confirm the presence of an optical PWN around PSR J0205+6449 and give an upper limit of m R≈ 24 for the optical magnitude of the pulsar. Furthermore, we make the tentative suggestion that our object o1, with an m R≈ 24.08, is the optical counterpart. If confirmed, the pulsar would have an L R/ LX≈ 0.004 and an optical efficiency of about five per cent of the Crab pulsar. Such a low efficiency is more consistent with the characteristic age of the pulsar rather than that of SN 1181. [ABSTRACT FROM AUTHOR]

We present high- and medium-resolution spectroscopic observations of the cataclysmic variable BF Eridani (BF Eri) during its low and bright states. The orbital period of this system was found to be 0.270881(3) d. The secondary star is clearly visible in the spectra through the absorption lines of the neutral metals Mg i, Fe i and Ca i. Its spectral type was found to be K3±0.5. A radial velocity study of the secondary yielded a semi-amplitude of . The radial velocity semi-amplitude of the white dwarf was found to be from the motion of the wings of the Hα and Hβ emission lines. From these parameters, we have obtained that the secondary in BF Eri is an evolved star with a mass of , whose size is about 30 per cent larger than a zero-age main-sequence single star of the same mass. We also show that BF Eri contains a massive white dwarf , which allows us to consider the system as a Type Ia supernova progenitor. BF Eri also shows a high γ-velocity and substantial proper motion. With our estimation of the distance to the system , this corresponds to a space velocity of ∼350 km s−1 with respect to the dynamical local standard of rest. The cumulative effect of repeated nova eruptions with asymmetric envelope ejection might explain the high space velocity of the system. We analyse the outburst behaviour of BF Eri and question the current classification of the system as a dwarf nova. We propose that BF Eri might be an old nova exhibiting ‘stunted’ outbursts. [ABSTRACT FROM AUTHOR]

We report simultaneous photometric and echelle-spectroscopic observations of the dwarf nova BZ UMa during which we were lucky to catch the system at the onset of an outburst, the development of which we traced in detail from quiescence to early decline. The outburst had a precursor, and was of a short duration (∼5 d) with a highly asymmetrical light curve. On the rise we observed a ‘jump’ during which the brightness almost doubled over the course of half an hour. Power spectra analysis revealed well-defined oscillations with period of ∼42 min. Using Doppler tomography we found that the unusual emission distribution detected in quiescence held during the outburst. After the maximum a new emission source arose, from the inner hemisphere of the secondary star, which became the brightest at that time. We analyse this outburst in terms of ‘inside-out’ and ‘outside-in’ types, in order to determine which of these types occurred in BZ UMa. [ABSTRACT FROM AUTHOR]

We present the analysis of high-speed photometric observations of FS Aurigae taken with the 4.2-m William Herschel Telescope and the high-speed camera ULTRACAM in late 2003. These observations were intended to determine whether there was any evidence of photometric variability with a period in the range 50–100 s. The discovery of such variations would help to explain the existence, in FS Aur, of the very coherent photometric period of 205.5 min that exceeds the spectroscopic period by 2.4 times. Such a discrepancy in the photometric and spectroscopic periods is unusual for a low-mass binary system that is unambiguously identified as a cataclysmic variable. Using various methods, including wavelet analysis, we found that with exception of the 205.5-min periodicity, the main characteristic of variability of FS Aur is usual flickering and quasi-periodic oscillations. However, we detected variability with a period of ∼101 and/or ∼105 s, seen for a short time every half of the orbital period. These oscillations may be associated with the spin period of the white dwarf (WD), not ruling out the possibility that we are observing a precessing rapidly rotating WD in FS Aur. [ABSTRACT FROM AUTHOR]