| Dwarf novae belongs to the semi-detached close binary stars,which is a subtype of cataclysmic variable star.According to the different characteristics of light variation,dwarf novae can be divided into three main subtypes:Z Cam,SU UMa and U Gem.Due to the frequent characteristics of dwarf novae outburst,its an ideal laboratory for studying the evolution model of cataclysmic variables.Due to the change in the geometrical position of the binary star system,when the orbital inclination of the binary star is greater than a certain critical value,the binary stars will obscure each other during their motion,which is called eclipse.The orbital period of the binary star can be accurately determined through the observed eclipse curve.When the eclipse curves of different parts of the binary star can be clearly distinguished,the eclipse curves of different parts can be analyzed to determine the mass,radius and other parameters of each part of the binary star.Therefore,the eclipse properties of binary stars provide an excellent window for people to study cataclysmic variable stars in depth.The orbital period distribution of dwarf nova has a typical period gap phenomenon in 2-3h,and the orbit is longer than 3h,which belongs to long-period dwarf novae.Dwarf novae are mainly distributed under the period gap,and the study of long-period dwarf novae is of great value.This paper is based on the research status of dwarf novae at home and abroad,the public data of K2,TESS space telescope and AAVSO,the characteristics of frequent eruptions of dwarf novae,the uniqueness of long-period dwarf novae,using the mature O-C method and time-varying curve analysis method,to study the orbital period variation and light variation characteristics of the long-period eclipsed dwarf nova sample stars V729 Sgr,GY Cnc,IP Peg and HS2325+8205.The article structure is as follows:The first chapter introduces the research status of dwarf novae,including the basic characteristics and classification of dwarf novae,the accretion disk instability model used to explain the explosion of dwarf novae,the orbital period gap in the dwarf novae evolution model,and the variation of the orbital period of dwarf novae Research.Finally,the research status of dwarf novae in X-ray,radio and jet are introduced.The second chapter mainly studies the statistical properties of dwarf novae.First,based on the statistics of 616 dwarf novae with known orbital periods in the dwarf novae catalog by Otulakowska-Hypka et al.(2016),it is further verified that the orbital period of dwarf novae has obvious periodic vacancy in 2-3h,which is consistent with the current research theory,67.7%of the dwarf novae are distributed under the period gap,and only 22.2%of the dwarf novae have a period greater than3h.Secondly,based on the current published cataclysmic variable star catalog and the latest research results,the eclipse dwarf novae are counted.Statistically found 103 eclipsed dwarf novae,including 68short-period eclipsed dwarf novae and 36 long-period eclipsed dwarf novae.Finally,the study of the dwarf nova material transfer rate is introduced,and its calculation and research methods are analyzed.The third chapter mainly studies the four sample stars(V729 Sgr,GY Cnc,IP Peg and HS 2325+8205)of long-period eclipse dwarf novae.Through the study of V729 Sgr,it is found that its orbital period has periodic changes,and the period and amplitude are?9.64 years and?442.37s,respectively.According to the interpretation of the orbital period oscillation of V729 Sgr by light travel-time effect,when the third object is coplanar with the central system,the third object may be a low-mass star.In addition,QPOs with a period of?1030-3370s were found for the first time in V729 Sgr.It was finally found that the V729Sgr had a negative superhump when it was quiescence.Different from the study of Ramsay et al.(2017),there is still a negative superhump at the first quiescence,but the intensity is relatively weak,which proves that the negative superhump is permanent in the quiescence of V729 Sgr.Through the analysis of the observation data of AAVSO and the available historical minimum time,the O-C method is used to find that the change rate of the orbital period of GY Cnc is+2.078×10-10 ss-1,and there may be periodic oscillation of the orbital period,Period and amplitude are?7.513 years,?228.96 seconds,respectively.Through the study of the orbital period variation of IP Peg,it is found that IP Peg may have orbital period periodic oscillation with a period of?13.188 years and an amplitude of?177.984 s.However,due to the lack of data,this result needs further observation and research to verify.Finally,through the study of HS 2325+8205,it is found that the orbital period of HS2325+8205 increases for a long time,and the orbital period changes rate to be·P=+1.47(±0.17)×10-10ss-1.In addition,the orbital period has periodic variation with period and amplitude of?10.73 years and?61.79s,respectively.Both the Applegate's mechanism and the light travel-time effect can explain the periodic variation of the orbital period of HS2325+8205.According to the interpretation of the orbital period oscillation of HS 2325+8205 by the light travel-time effect,when the orbital inclination of the third object is greater than?24.11°,the third object may be a brown dwarf.The fourth chapter firstly summarizes the work,then analyzes the existing problems,and finally looks forward to the later work. |
PDF Full Text Request