Progress has been made in the study of quasi-periodic oscillations of cataclysmic variable stars

Recently, Sun Qibin, a doctoral student in the Yunnan Astronomical Observatory of the Chinese Academy of Sciences, and Qian Shengbang, a supervisor, have made new progress in the study of quasi-periodic oscillations (QPOs) of cataclysmic variable stars (QPOs). Using TESS’s survey data, the work discovered QPOs with a period of about 2160 seconds for the first time during the explosion of the long-period dwarf nova HS 2325+8205, and found that the oscillation intensity of QPOs is related to orbital phase. The discovery of the correlation between orbital phase and the oscillation intensity of QPOs provides a new way to study the origin of QPOs in cataclysmic variable stars. The results were published online Dec. 5 in the Monthly Notices of the Royal Astronomical Society, an international astronomical journal.

A dwarf nova is a subtype of cataclysmic variable star , a semi-contiguous close binary star consisting of a weakly magnetic ( Bsurface < 106G ) white dwarf primary star , which fills the Roche lobe and transfers material to the primary star , with angular momentum forming an accretion disk around the white dwarf and colliding with the accretion disk to form a bright , hot spot ( see Figure 1 ) . The new dwarf system exhibits intermittent bursts , with luminosity increasing by about 2-8 magnitudes over days to weeks, bursts lasting from a few days to dozens of days, and re-emission times ranging from days to years. In addition to outbursts, dwarf novae are generally thought to have three types of rapid oscillations: DNOs: Dwarf Novae Oscillations, long-period Dwarf Novae Oscillations, and QPOs. QPOs have longer periods than DNOs, ranging from hundreds of seconds to thousands of seconds. QPOs are widely found in cataclysmic variable stars with high material transfer rates, such as nova-like and bursting dwarf novae, and the origin of QPOs is closely related to accretion disks, but the specific physical process of the origin of QPOs remains controversial. QPOs are an important characteristic of cataclysmic variable stars, and the study of the origin of QPOs is of great significance for improving the evolution model of accretion disks of cataclysmic variable stars.

Figure 1: Basic structure of a cataclysmic variable star. This image was made by Rob Hynes (see

Based on TESS photometric data and LSP (Lomb–scargle periodogram) and CWT (Continuous Wavelet Transform) methods, this work found for the first time that HS 2325+8205 has QPOs of ~2160s during long bursts, which is consistent with current research theory. By comparing the oscillation intensity and orbital phase of QPOs of HS 2325+8205, it can be found that they have a strong correlation, and their oscillation intensity is stronger in the 0.5-0.9 phase than the 0.1-0.5 phase, and the strongest extra-food curve is the weakest in the orbital phase of about 0.5 (see Figure 2). Based on the relationship between orbital phase and the oscillation intensity of QPOs, this work excludes the effects of irradiation and elliptic modulation of secondary stars, but whether hot spots excluded from the origin of QPOs have an effect on the oscillation intensity needs to be further studied. In addition, the work also found a significant double hump phenomenon in HS 2325+8205, with three different types of eruptions and an outbreak period of about 13.83 days.

Figure 2: CWT two-dimensional power spectrum and its corresponding optical curve. The selected part of the rectangular box is where the intensity of QPOs is greatest.

This work was supported by the National Natural Science Foundation of China. (Source: Yunnan Astronomical Observatory, Chinese Academy of Sciences)

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