Intranight flickering of RS Ophiuchi: II. Exponentially distributed quasiperiod modes
Abstract
Linearized and flattened light curves (29 in B band and 29 in V band) of the recurent nova RS Oph, taken in 20082017 by 5 telescopes, are analyzed. The purposes are (i) characterizing of the flickering phenomenon by various ways and (ii) justification of the "resonance" distribution of the modes of the flickering quasiperiods, found in Paper I. The typical observing circumstances are: monitoring duration 60150 min, number of CCD frames 50200 and time step 0.51.5 min.
Part 1 presents photometric diagrams, standard and range deviations of the light curves in dependence on the average flux, as well as the distributions of the skewness and kurtosis of the histograms of the light curves. The intranight flickering contains local disk obscures/shots and global disk instabilities. It seems both processes alternate their superiority. The average skewness, 0.12±0.30, gives weak privilege to the local shots. The average kurtosis, 0.17±0.62, gives some privilege to the global instabilities. In contrast to the random process with bellshaped distribution of the deviations, deficit of small and large deviations is obvious in about 1/2 of the cases. Presence of light variations, close to oscillations, give some priority to the global disk instabilities.
In Part 2 every light curve is scanned digitally by a system of data windows with sizes Θ. Six fractal parameters are derived as average values for each Θ and regarded as functions on Θ in loglog coordinates. The average structure gradient, 0.48±0.16, also does not point out the prior process of the light variations. The mean value of the Hurst gradient, 0.22 ± 0.06, giving fractal dimension 1.78 ± 0.06, corresponds to autocorrelation at short time scale. The mean value of the fractal dimension, 1.48 ± 0.06, too. The asymmetry function, introduced in this work, shows that the mean duration of the elementary shots is 3.6±0.8 min. It seems the relatively weak and short local shots dominate at time scales of a few minutes.
Part 3 presents 97 quasiperiods and their distributions. The quasiperiods are detected by the local minima of the structure functions as 58 primary, 20 secondary, 10 tertiary and 13 very short. All quasiperiods are confirmed by the local maxima of the relevant autocorrelation function. The distribution of the quasiperiods shows 6 modes, at 8, 13, 21, 30, 48 and 73 min. The modes of the quasiperiod P follow exponential (or power) function on the number of the mode M with standard deviation of 4.7%. The power dependence is P_M=3.48× 1.55^M. This function predicts modes also at 3.5, 5.3 and 115 min, which are not detected in this work. However, the characteristic duration of the elementary shot, 3.6±0.8 min, corresponds well to the predicted mode at 3.5 min. Because 1.55 ≈ 3/2, the modes of the quasiperiods like obey 3/2 resonance with unknown reason. The relative energy of the quasiperiod (i.e. of the quasiperiodic structure, including the energy of its substructures) correlates with the logarithm of the quasiperiod under a slope coefficients 0.02.
Generally, the flickering light curves are too complicated and various, without a possible classification (at least in the present work). Unique systematic is only the resonancelike sequence of the quasiperiod modes.
 Publication:

Bulgarian Astronomical Journal
 Pub Date:
 February 2020
 Bibcode:
 2020BlgAJ..32...35G
 Keywords:

 stars: binaries: symbiotic;
 novae;
 cataclysmic variables;
 accretion;
 accretion discs;
 stars: individual: RS Oph