Cataclysmic variable stars (CVs) are binary system that is consisted with a white dwarf (WD) and a late spectral Roche-lobe filling star. Because of the angular momentum loss due to the magnetic braking and the gravitational radiation, the orbital separation decreases which leads to the mass transfer. As a subclass of CVs, polars, except the general evolution trace with CVs, have their own peculiarities given their high magnetics, such as no-disk accretion and synchronous rotation. Without the modulation of disk to mass transfer, the radiation magnitude of system is related to the mass accretion rate, and observation of more than one hundred years implies mass transfer rate variation in short timescale superimposed on the secular that, which causes the state switch between high and low. This thesis summarizes the characteristics of the standard model about the evolutionary of CVs and accretion model for polars. Next, we, from the twelve observations of MN Hya, obtain a series of results listed below:1. The mass of WD in MN Hya is about $0.95M_{\odot}$, which is above the mean mass $0.75M_{\odot}$;Because there was a LC of low-state system which give the information restricting the time length for the WD ingress and egress, we can induce the size of the WD and infer it mass in accordance to the mass-radius relation of helium WD. The mass of this WD is about $0.95M_{\odot}$ which is above the mean mass $0.75M_{\odot}$.2. The optical radiation from MN Hya shows no periodical variation except orbital one like that of the X-ray;When the system was in high state and the flickering sticked out with time scale of several minutes, but we use the DFT to search the frequency and find nothing new, which means the flickering is random like that of X-ray.3. MN Hya is one-pole accretion system;The dominant radiation hump near phase 0.7 of high-state LCs disappears when the system is in low state. which is so not compatible with the two-pole model and we think MN Hya is one-pole accretion system.4. The mass transfer rate of MN Hya is related with the magnitude of fast intensity variation;We analysis the eclipsing profiles and compare these with the corresponding intensity of the flickering. The intensity of flickering reduced when the accretion rate is higher, which implies the mass transfer rate of MN Hya is related with the magnitude of fast intensity variation.5. When MN Hya is in high stats, the minimum time is not in accordance with the mid-eclipse time of WD.The high precise photometry gives the time interval of about 3 seconds when the system is in high state while more than 20 seconds when it is in low state, so the light minimum time is not the medium eclipsing time of the WD when the system is in high state.
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