Searching for flickering statistics in T CrB

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 11/2009; DOI: 10.1111/j.1365-2966.2009.16068.x
Source: arXiv

ABSTRACT We analyze $V$-band photometry of the aperiodic variability in T CrB. By applying a simple idea of angular momentum transport in the accretion disc, we have developed a method to simulate the statistical distribution of flare durations with the assumption that the aperiodic variability is produced by turbulent elements in the disc. Both cumulative histograms with Kolmogorov-Smirnov tests, and power density spectra are used to compare the observed data and simulations. The input parameters of the model $R_{\rm in}$ and $\alpha$ are correlated on a certain interval and the most probable values are an inner disc radius of $R_{\rm in} \simeq 4 \times 10^9$ cm and a viscosity of $\alpha \simeq 0.9$. The disc is then weakly truncated. We find that the majority of turbulent events producing flickering activity are concentrated in the inner parts of the accretion disc. Comment: 9 pages, 10 figures, accepted for publication in MNRAS

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    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 alpha = 0.10 - 0.40 and an inner disc truncation radius in the range R_in = 0.88 - 1.67 x 10^9 cm. The exact values depend on the mass transfer rate in the sense that alpha decreases and R_in increases with mass transfer rate. In any case, the inner disc radius found for KR Aur is considerably smaller than in 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.
    Monthly Notices of the Royal Astronomical Society 11/2011; 420(3). · 5.52 Impact Factor
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    ABSTRACT: We present high cadence (1-10 hr^-1) time-series photometry of the eruptive young variable star V1647 Orionis during its 2003-2004 and 2008-2009 outbursts. The 2003 light curve was obtained mid-outburst at the phase of steepest luminosity increase of the system, during which time the accretion rate of the system was presumably continuing to increase toward its maximum rate. The 2009 light curve was obtained after the system luminosity had plateaued, presumably when the rate of accretion had also plateaued. We detect a 'flicker noise' signature in the power spectrum of the lightcurves, which may suggest that the stellar magnetosphere continued to interact with the accretion disk during each outburst event. Only the 2003 power spectrum, however, evinces a significant signal with a period of 0.13 d. While the 0.13 d period cannot be attributed to the stellar rotation period, we show that it may plausibly be due to short-lived radial oscillations of the star, possibly caused by the surge in the accretion rate.
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    ABSTRACT: Recently, wavelets and R/S analysis have been used as statistical tools to characterize the optical flickering of cataclysmic variables. Here we present the first comprehensive study of the statistical properties of X-ray flickering of cataclysmic variables in order to link them with physical parameters. We analyzed a sample of 97 X-ray light curves of 75 objects of all classes observed with the XMM-Newton space telescope. By using the wavelets analysis, each light curve has been characterized by two parameters, alpha and Sigma, that describe the energy distribution of flickering on different timescales and the strength at a given timescale, respectively. We also used the R/S analysis to determine the Hurst exponent of each light curve and define their degree of stochastic memory in time. The X-ray flickering is typically composed of long time scale events (1.5 < alpha < 3), with very similar strengths in all the subtypes of cataclysmic variables (-3 < Sigma < -1.5). The X-ray data are distributed in a much smaller area of the alpha-Sigma parameter space with respect to those obtained with optical light curves. The tendency of the optical flickering in magnetic systems to show higher Sigma values than the non-magnetic systems is not encountered in the X-rays. The Hurst exponents estimated for all light curves of the sample are larger than those found in the visible, with a peak at 0.82. In particular, we do not obtain values lower than 0.5. The X-ray flickering presents a persistent memory in time, which seems to be stronger in objects containing magnetic white dwarf primaries. The similarity of the X-ray flickering in objects of different classes together with the predominance of a persistent stochastic behavior can be explained it terms of magnetically-driven accretion processes acting in a considerable fraction of the analyzed objects. Comment: 10 pages, 3 figures, 2 tables. Language revision. Accepted for publication in A&A
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