A flickering study of nova-like systems KR Aur and UU Aqr

Authors

  • A. Dobrotka,

    Corresponding author
    1. Department of Physics, Institute of Materials Science, Faculty of Materials Science and Technology, Slovak University of Technology in Bratislava, Jána Bottu 25, 91724 Trnava, Slovak Republic
    2. Department of Astronomy, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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  • S. Mineshige,

    Corresponding author
    1. Department of Astronomy, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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  • J. Casares

    Corresponding author
    1. Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
    2. Departamento de Astrofísica, Universidad de La Laguna, Avda. Astrofísico Francisco Sánchez s/n, E-38271 La Laguna, Tenerife, Spain
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E-mail: andrej.dobrotka@stuba.sk (AD); shm@kusastro.kyoto-u.ac.jp (SM); jcv@iac.es (JC)

ABSTRACT

We present a study of the flickering activity in two nova-like systems, KR Aur and UU Aqr. We applied a statistical model of flickering simulations in accretion discs based on turbulent angular momentum transport between two adjacent rings with an exponential distribution of the turbulence dimension scale. The model is based on a steady-state disc model, which is satisfied in the case of hot ionized discs of nova-like cataclysmic variables. Our model successfully fits the observed power-density spectrum of KR Aur with the disc parameter α= 0.10–0.40 and an inner-disc truncation radius in the range Rin= 0.88–1.67 × 109 cm. The exact values depend on the mass-transfer rate in the sense that α decreases and Rin increases with mass-transfer rate. In any case, the inner-disc radius found for KR Aur is considerably smaller than those for quiescent dwarf novae, as predicted by the disc instability model. On the other hand, our simulations fail to reproduce the power-density spectrum of UU Aqr. A tantalizing explanation involves the possible presence of spiral waves, which are expected in UU Aqr because of its low mass ratio but not in KR Aur. In general our model predicts the observed concentration of flickering in the central disc. We explain this by the radial dependence of the angular-momentum gradient.

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