| 其他摘要 | Cataclysmic variable stars (CVs) are semi-detached close binary systems consisting of a white dwarf (primary) and a late main-sequence star (secondary) filled with the Roche lobe, including important subtypes such as novae, recurrent novae, nova-like stars, dwarf novae (DNe), and magnetic CVs. When the magnetic field of the white dwarf is weak, an accretion disk forms; when the magnetic field is strong, the accretion curtains or accretion columns may form. Numerous phenomena in CVs are associated with the matter motion and the accretion disk instability, such as outbursts, rapid oscillations, accretion disk precession, magnetically controlled accretion and orbital evolution. A well-known observational feature of CVs is the significant drop in time between 2 and 3 hours, known as the orbital period gap. Long-period CVs are systems that are above the gap and have periods longer than 3 hours. These CVs usually have higher matter accretion rates and hotter and larger-scaled accretion disk than short-period CVs, and are natural laboratories for the study of tne matter motion and the accretion disk instability. In addition, accretion is one of the most important physical processes in astronomy and is prevalent in celestial systems of different scales, such as CVs, X-ray binaries, protostars, and active galactic nuclei. The complex structural features of the accretion disk in long-period CVs make it the most ideal place to study accretion processes in astrophysics. At the same time, some long-period CVs, such as recurrent novae, may be the precursors of type Ia supernovae due to their large mass white dwarfs and high accretion rates. This makes the study of long-period CVs of great scientific significance and value. However, due to the limitations of observations, especially the lack of high-precision continuous data, there is a lack of studies on the matter motions and accretion disk instabilities in long-period CVs, which severely limits the progress of research in the related fields. The authors have seized the valuable opportunity of the data release from space survey telescopes, such as K2 and TESS, to analyze and study the outbursts, quasi-periodic oscillations, super-orbital signals (SOR), positive superhumps (PSH), negative superhumps (NSH), and orbital period variations of long-period CVs, and to investigate the matter motion and accretion disk instability in long-period CVs, relying on the high-precision continuous photometric data from these telescopes. The main research results are as follows: （1）The SOR and NSH in CVs are usually thought to originate from the reverse precession of the tilted disk, however, there is a lack of conclusive evidence. Based on K2 and TESS photometry, this paper found SOR, NSH, and PSH with periods of 3.0451(5), 0.152047(2), and 0.174686(7) days, respectively, in SDSS J0812. In addition, we find the periodic variations of 3.045(8), 3.040(6), and 3.053(8) days in the eclipse minima eclipse depths, and NSH amplitudes, respectively. These variations reach a maximum at the ~ 0.75 phase of the tilted disk precession, providing new evidence for a tilted disk precession. In this study, we find that the amplitude of the NSH varies periodically in response to the superorbit signal, which is strong evidence for the existence of a direct correlation between the origin of the NSH and tilted disk precession. （2）As a subtype of CVs, intermediate polars (IPs) have magnetic field strengths between 1-10 MG. As the inner disk of the accretion disk is truncated by the strong magnetic field, the streams along the magnetic lines of force to the magnetic poles form the accretion curtains. Currently, there is a paucity of studies on accretion curtains, and direct evidence to confirm their existence is lacking. Based on the TESS data, we find that the O-C of the eclipse minima and the NSH amplitude show periodic variations, with periods of 3.939(25) and 3.907(30) days, respectively.In addition, this paper finds for the first time that the eclipse depth of TV Col exhibits a bi-periodic variation with periods of P1= 3.905(11) d and P2 = 1.953(4) d, where P2 is about half of the period of P1 and the disk precession, respectively. We suggest that P1 may originate from periodic variations in the brightness of the eclipse center due to tilted disk precession, while P2 is related to the properties of IPs, and may originate from variations of the two accretion curtains in response to tilted disk precession. The discovery of this double-periodic variation phenomenon may indirectly prove the existence of the accretion curtains, providing a new perspective and way to study the IPs and the tilted disk precession. （3）DN outbursts are usually thought to be caused by the thermal instability of the accretion disk, where the viscous dissipation on the accretion disk triggers a series of physical changes, while the NSH originates from the interaction of the tilted disk precession with the streams from the secondary star. However, the combination of thermally unstable disk and tilted disk has been understudied. Based on the TESS data, NSH with a period of 0.24497(1) days is found, and the amplitude of NSH is observed to vary with the outburst. Therefore, we suggest that the relationship between NSH amplitude and outbursts can serve as an important window to study accretion disk instability and the origin of NSH. In addition, this study finds the ~ 2800 s QPOs at the top of a long outburst of AH Her, similar to that of HS 2325+8205. This finding suggests that the presence of QPOs at the top of long outbursts of Z Cam-type DNe may be common. （4）It has been more than forty years since the first negative superhump was discovered, yet the number of discovered systems is only about a hundred, which makes the negative superhump phenomenon particularly rare compared to the tens of thousands of CVs. In this paper, based on TESS photometry, nine new long-period negative superhump systems have been discovered, namely ASAS J1420, TZ Per, V392 Hya, ASASSN-V J1137, ASASSN-V J0611, 2MASS J0715, LAMOST J0925, ASASSN-17qj, and ZTF18acakuxo. It is noteworthy that the orbital periods of seven of these CVs were determined by us. These new discoveries not only enrich the sample of negative superhumps, but also provide indispensable data support for further investigation of their physical properties and evolutionary mechanisms. （5）Among CVs, QPOs are rapid oscillation phenomena with small amplitudes, whose period ranges are usually between a few hundred and a few thousand seconds. Although it is widely believed that this oscillation phenomenon is closely related to high matter transfer rates and accretion disk, there are still many controversies about the exact mechanism. Based on the TESS photometry, we find for that a QPO with a period of about ~ 2160 s in the long outburst of HS 2325+8205. It is worth mentioning that a correlation between the oscillation strength of QPOs and the orbital phases has been found. Therefore, we propose that the relationship between orbital phases and QPOs can serve as an important window to study the origin of QPOs and the matter motion on the accretion disk. |
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