Browsing by Subject "Cataclysmic variable stars"

Now showing 1 - 5 of 5
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    A cataclysmic key program for SALT
    (2006) Warner, Brian
    The study of cataclysmic variable stars has a long history in South Africa. A brief overview of this history is followed by indications of where the new Southern African Large Telescope (SALT) is likely to make major contributions to this research field. There are about 60 staff and students in the SALT Consortium, who work on interacting binaries containing compact components. Most of these people work on cataclysmic variable stars, with the remainder researching neutron star and black hole binary pairs. This group will use a significant amount of SALT observing time. I look at some of the collective and individual topics that SALT will be able to address.
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    Atomic processes in nova shells
    (1990) Smits, Derck Peter; Warner, Brian
    The unusual spectra of the spatially-resolved nova shells of DQ Her, T Aur and CP Pup are reviewed. Because calculations for these conditions have not been made, recombination models of HI, HeI and CNO from a neutral to a doubly ionized state were constructed. The models are described and the results presented for densities at various temperatures. A photoionization model is also described. The effects of non-uniform density distributions in nova shells have been investigated and the observational consequences discussed. A model of the CP Pup shell is described and the evolution of this plasma during the nova's constant luminosity phase traced. The properties of neon novae are summarized and compared with the features seen in the optical spectra of old classical novae. Enhanced neon abundances are used in the model of the CP Pup Shell to investigate its effect on the evolution of the shell. Finally, the results of some near-infrared observations made on the shells of CP Pup, RR Pic and T Pyx are reported.
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    High-speed photometry of SDSS J013701.06 − 091234.9
    (2004) Pretorius, M L; Woudt, P A; Warner, B; Bolt, G; Patterson, J; Armstrong, E
    We present high speed photometry of the Sloan Digital Sky Survey cataclysmic variable SDSS J013701.06-091234.9 in quiescence and during its 2003 December superoutburst. The orbital modulation at 79.71pm0.01 min is double humped; the superhump period is 81.702pm0.007 min. Towards the end of the outburst late superhumps with a period of 81.29pm0.01 min were observed. We argue that this is a system of very low mass transfer rate, and that it probably has a long outburst interval.
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    Hubble Space Telescope and Optical Observations of Three Pulsating Accreting White Dwarfs in Cataclysmic Variables
    (2007) Szkody, Paula; Mukadam, Anjum; Gänsicke, Boris T; Woudt, Patrick A; Solheim, Jan‐Erik; Nitta, Atsuko; Sion, Edward M; Warner, Brian; Sahu, D K; Prabhu, T; Henden, Arne
    Ultraviolet observations using the Solar Blind Channel on the Hubble Space Telescope provide light curves and low-resolution spectra of three pulsating white dwarfs in the cataclysmic variables SDSS J013132.39-090122.3, SDSS J161033.64-010223.3, and SDSS J220553.98+115553.7. The UV light curves show enhanced pulsation amplitudes over those from simultaneous and previous optical photometry, while the UV-optical spectra are fit with white dwarf temperatures near 15,000 K. These temperatures place the accreting white dwarfs outside the instability zone for noninteracting DAV white dwarfs and show that the instability strip is complex for accreting white dwarfs
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    QPOs in cataclysmic variables and in X-ray binaries
    (2005) Kluźniak, W; Lasota, J-P; Abramowicz, M A; Warner, B
    Recent observations, reported by Warner and Woudt, of Dwarf Nova Oscillations (DNOs) exhibiting frequency drift, period doubling, and 1:2:3 harmonic structure, can be understood as disc oscillations that are excited by perturbations at the spin frequency of the white dwarf or of its equatorial layers. Similar quasi-periodic disc oscillations in black hole low-mass X-ray binary (LMXB) transients in a 2:3 frequency ratio show no evidence of frequency drift and correspond to two separate modes of disc oscillation excited by an internal resonance. Just as no effects of general relativity play a role in white dwarf DNOs, no stellar surface or magnetic field effects need be invoked to explain the black hole QPOs.