| Radio-type dwarf nova is a kind of dwarf nova system with radio radiation.It is a semi-connected binary star system composed of a white dwarf and a late-type main sequence star fills its Roche lobe.It is difficult to observe the radio radiation of such celestial bodies,generally which need two conditions meet at the same time.One is that the radio telescope is large enough,and the other is that the timing of the observation is just when the dwarf nova outbursts.The white dwarf of dwarf novae has a weak magnetic field.The material transferred from the red dwarf will form an accretion disk around the white dwarf.Due to material accumulation and thermal viscosity instability,the material on the accretion disk will quickly fall to the surface of the white dwarf and be released.The emergence of gravitational potential can increase the brightness,and this phenomenon is called an explosion.Outbursts of Dwarf novae are unpredictable.All radio radiations observed so far are during outburst,and the radio radiation must be generated during a certain process in the explosion.Due to the shortage of radio observation resources,it is necessary to conduct optical research on radio dwarf novae and provide more candidates,provide a basis for radio observation.By analyzing the photometric data of radio-type dwarf novae,a series of new discoveries have been obtained.The research results obtained are as follows:1.U Gem is a dwarf nova prototype star with an orbital period longer than the period gap.From its discovery to now,it has accumulated a large amount of photometric data.Using the data of predecessors and our latest observations for a total of nearly 60 years,it was discovered that the orbital period of is increasing with the rate P=1.19(±0.23)×10-9 d/yr.Moreover,the O-C data has significant orbital periodic oscillations.Research has found that the periodic oscillations may be caused by the existence of a third celestial body or the magnetic activity of the secondary star.2.Using a large amount of data on the website of American Association of Variable Star Observers(AAVSO),we collected the light curves of U Gem at different stages of the outburst and found that the eclipse depth became shallower during the outburst.And in the event of an outburst,the eclipsing time will be advanced or delayed.Quasi-periodic oscillations(QPO)are found in multiple light curves.The circumference of these QPOs is generally a few hundred seconds,and some have strong coherence and some are weak.It is generally believed that QPO originates from the activity on the accretion disk.3.EM Cyg is a deep eclipse dwarf nova.We removed the minimum moment of the outburst from the previous data and re-analyzed the orbital period.The study found that the orbital period of the system is increasing at the rate P=1.66(±0.36)×10-8 d/yr.A third celestial body with an eccentricity of 0.63 and a period of 26.14(±0.75)years was found in EM Cyg.The celestial body may be a K-type or M-type star.4.The 28-day continuous observation of EM Cyg by the Transiting Exoplanets Survey Satellite(TESS)covered a complete outburst.After removing the profile of the outburst,it is found that the depth of the eclipse will gradually become deeper during the outburst.The O-C analysis using the outburst data observed by TESS found that the minimum time of eclipse during the outburst in this system will be advanced.For the first time,we have studied the QPO evolution of EM Cyg in an outburst using wavelet analysis.There are two QPOs in the light curves,one is a long-term QPO with a period of about 1000s.The other only appears during outburst,with a period of about 500s.These two QPOs have a strong phase dependence.The 1000s QPO appears near the 0.25 and 0.75 phases,and the 500s QPO only appears near the 0.5 phase.The phases of these two QPOs are not the same,which may originate from different parts of the accretion disk.5.The relationship among the outburst waiting time,amplitude,total flux,and outburst duration of the dwarf nova SS Cyg was counted.It was found that the outburst period and amplitude of this source did not conform to the K-P relationship.There are two distinct outbursts in SS Cyg,and the outburst mechanism may be different.Most of the outbursts with radio radiation discovered so far are in the long outbursts. |
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