| 其他摘要 | The three types periodic oscillations as a typical photometric feature of cataclysmic variables(CV) discovered in decades ago is the rapid changes of luminosity in the optical band.With the different time scale and coherence, there are dwarf nova oscillations(DNO), quasi-periodic oscillations(QPO), and longer period dwarf nova oscillations(lpDNO). It is generally believed that the physical origin of three periodic oscillations may be closely related to the accretion process of compact stars. Thus, they can provide abundant information and clues for the study of white dwarf accretion. There are two main works in this paper about the three periodic oscillations and accretion of CV.On one hand， the three periodic oscillations of CV are investigated. On the other hand,the oscillations of a newly discovered dwarf Nova J0426 are studied. There are some results as follow:1. By investigating the oscillation characteristics of different subtypes of CV, we found that DNO and QPO mainly present in the light curves of novae, and the period of dwarf Nova oscillation is usually 100 - 400 s, which is the remarkable feature of this subtype. The quasi-periodic oscillation are dominated by kilosecond QPO. None oscillations are found in recurrent novae, but another irregular light variation are observed called flickering. All three types oscillations usually appear in the outburst process of dwarf nova. U Gem and Z Cam dwarf novae are dominated by DNO, while SU UMa are dominated by DNO and DNO-related QPO. In nova-like, DNO usually occur in high brightness states and exists intermittently, rarely are observed in low brightness state ofVY Scl type nova-like, and kilosecond QPO occur almost in RW Sex stars. The oscillations of polars are mainly QPO, a special oscillation occurring only in this type have been found. It’s period is usually 1-3 seconds, which is called ”noisear”. For intermediate polars, a special periodic oscillation called transient periodic oscillation are found in the object DO Dra which was observed in intermediate brightness state(between quiescence and outburst). The differences between transient periodic oscillation and QPO lie in the varying amplitude and invariable phase.2. Many physical mechanism have been proposed to explain the origin of three types periodic oscillations. For example, white dwarf pulsations, it is proposed to use the pulsation of nonradial g mode to explain DNO, because its period is just in line with the period of dwarf nova oscillation; Accretion disk pulsation can modulate the brightness through reflection, obscuring and the brightness change caused by unstable accretion flow of material on the edge of the inner accretion disk, which may be the source of oscillation.The hot spots on the accretion disk, which are periodically obscured by white dwarfs, also produce brightness modulation. The origin of the oscillations may be related to magnetically channeled accretion, for polars the optical DNO can be generated by reprocessing the X-ray radiation from the white dwarf’s accretion column. The low inertia magnetic accretor model can effectively combine three types of rapid oscillations.3. Photometric observation of SU UMa dwarf nova J0426 was studied. It found that there are not eclipses in the quiescence light curves which obtained by 80cm and 85cm telescopes, which don’t support the result of Kato’s research that J0426 is a grazing eclipse system. This shows the instability of the dwarf novae system J0426 and the complexity of the accretion system of the white dwarf. Since the eclipse is considered to occur in the zero phase, the eclipsed light source should be an unstable bright area related to the accretion process. The instability of accretion process reflects the instability of grazing eclipse . In order to further understand the accretion physics of J0426， Fourier transform analysis is used to study periodic oscillations. From the obtained Fourier spectrum, eight possible periodic signals are found. The analysis of these eight signals show that these signals are quasi-periodic oscillations. Among them, three signals have harmonics, that is f4 ≈ 2 × f2， f7 ≈ 2 × f3 and f8 ≈ 2 × f5, which belong to DNO-related QPO. And one oscillating signal with a period of 894 seconds is considered as kilosecond QPO. |
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