The Theoretical Study Of Symbiotic Stars

This paper is a theoretical doctorial thesis on the study of symbiotic stars. Their spectacular and photometric variability is a very important and attractive phenomenon. The spectra of symbiotic stars suggest that a three-component system consists of a binary with a hot component (white dwarf, neutron star or main-sequence star with an accretion disk ) and a cool component (red giant) and nebulae region. In this thesis, we summarize recent observational properties and theoretical study on symbiotic stars, and present the results of our studies on the field.By means of a population synthesis code, we have carried out a theoretical study of semi-detached symbiotic stars, detached symbiotic stars and D-symbiotic stars. In semi-detached symbiotic stars simulated by an accretion disks around main-sequence stars, there are two cases: dynamical unstable and stable Roche lobe overflow. To the first case, the birthrate of symbiotic stars is ⁰.056 — 0.045yr^-1 and the number is ⁵ in the Galaxy; to the stable Roche lobe overflow, the birthrate and the number are ⁰.002 -0.005yr^-1 and ⁶0—280, respectively. By comparison with observations and statistic analysis, we consider that AX Per & CI Cyg (as the only candidates of semi-detached symbiotic stars ) may not be semi-detached symbiotic stars. For detached symbiotic stars simulated by thermonuclear runways on the surface of white dwarf accretor, we estimate the total number and the birthrate of detached symbiotic stars in the Galaxy as 1,200 — 15,000 (it is 4,300 in standard model) and ⁰.035 —0.131yr^-1(it is 0.076yr^-1 in standard model), respectively. The theoretical estimate of the Galactic occurrence rate of symbiotic novae is ¹.3 —13.5yr^-1 (it is 3.4yr^-1 in standard model), out of which weak symbiotic novae comprise from ⁰.6 —6.0yr^-1(it is 1.5yr^-1 in standard model). In all model assumptions, two crucial physical parameters for determination of the birthrate and number of detached symbiotic stars and novae are efficiency of accretion by white dwarfs (which greatly depends on the outcome of common envelope evolution and stellar wind velocity)...