Multiple timescales in cataclysmic binaries

Abstract

Aims. We study the variability of the cataclysmic variable DO Dra, on time-scales of between minutes and decades. (15) d . We analyzed the profile of the "composite" (or "mean") outburst. We discovered however, that a variety of different outburst heights and durations had occurred, contrary to theoretical predictions. The analysis of the historical data has shown a correlation between the decay time dt/dm and the outburst maximum brightness with a slope d(dt/dm)/dm = 0.37(9). With increasing maximum brightness, we find that the decay time also increases; this is in contrast to the model predictions, which indicate that outbursts should have a constant shape. This is interpreted as representing the presence of outburst-to-outburst variability of the magnetospheric radius. A presence of a number of missed weak narrow outbursts is predicted from this statistical relationship. We tabulate characteristics of the "quasi-orbital" variations, which indicate that an amplitude maximum occurs between quiescence and the outburst peak. The semi-amplitude of the spin variability does not exceeded 0.02 mag. A new type of variability is detected, during 3 subsequent nights in 2007: periodic (during one nightly run) oscillations with rapidly-decreasing frequency from 86 to 47 cycles/day and a semi-amplitude increasing from 0. m 06 to 0. m 10, during a monotonic brightness increase from 14. m 27 to 14. m 13. This phenomenon was observed only during an unusually prolonged event of ∼1 mag brightening in 2007 (lasting till autumn), during which no (expected) outburst was detected. We refer to this behaviour as to the "transient periodic oscillations" (TPO). We attribute the frequency decrease to "beat"-type of the variability, probably caused by irradiation of a cloud that is spiralling down to the white dwarf. Its frequency would then increase and coverge towards the spin frequency. To study this new and interesting phenomenon, new regular photometric and spectral (in a "target of opportunity" mode) observations are required.

Quasi-Periodic Oscillation of a Magnetic Cataclysmic Variable, DO Draconis

“…Šimon (2000) discovered the ejection period of 870 day, and the magnitude decrease rate faster than that of non-magnetic structure. Andronov et al (2008) identified the ejection periods of 311 day ~ 422 day using the observation data obtained in 2006 ejection and confirmed that the quasiperiodic oscillations (QPOs) also exist in DO Dra.…”

“…4. Andronov et al (2008) pointed out that various QPOs and transient periodic oscillations (TPOs) exist in the observational data, but they could not found some periodicity of these QPOs. At this time, the observational data are not sufficient to confirm this periodicity.…”

“…QPOs were also observed at TT Ari (Tremko et al 1996;Andronov et al 1999;Smak 2014), and while QPOs in IP-type stars are believed to be generated by the bright bulb around the white dwarf with magnetic fields, detailed numerical calculation results have not been reported yet. These QPOs were discovered at DO Dra and Andronov et al (2008) also discovered disappearance of the QPOs at DO Dra and proposed to name this phenomenon as transient-periodic oscillations (TPOs).…”

“…The optical monitoring of MCVs has been performed in Korea since 1995 using domestic telescopes and as a part of "Inter-Longitude Astronomy" campaign (Andronov et al 2010), international observation monitoring was conducted and the analysis results have been reported (Andronov et al 2008(Andronov et al , 2011(Andronov et al , 2015Kim et al 2004Kim et al , 2005aKim et al , 2005bKim et al , 2009Yun et al 2011) While DO Dra, one of the target stars of ILA campaign, shows variable amplitude and ejection behavior with indeterminable periods, various periods and QPO phenomena obtained from photometric observation data of DO Dra have been analyzed and the results are presented in this study.…”

Long-term photometric behavior of the eclipsing cataclysmic variable V729 Sagittarii

“…We also used several more complete outbursts to estimate the parameters, which are listed in Table 1. It seems that the decay time is dependent on the magnitude at the maximum (see Table 1), which is similar the magnetic dwarf nova DO Dra (Andronov et al 2008). The nature of a rapid rise and a slower Apart from several normal outbursts, there are the smaller-amplitude outbursts (the solid asterisk) and dips.…”