Research on Star Formation and Associated Gas DynamicalPhenomena

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1. Equilibrium structure of rotating interstellar clouds has been investigated and the maximum mass of the cloud in equilibrium has been determined. 2. The stability of rotating clouds has been investigated by following the dynamical evolution of the cloud starting from the equilibrium state and it has been found that the cloud is unstble when the ratio of the semi-major axes exceeds about 4. 3. The dissipation processes of magnetic fields in the interstellar clouds have been investigated and it has been found that the magnetic field is well frozen to the gas at the density n_H 10^<11>cm^<-3>, decouples from the gas at n_H 5x10^<11>cm^<-3>, and recovers the coupling when the temperature T exceeds about 1000K. Therefore, most of the initial magnetic flux of the cloud is lost between the states of n_H 5x10^<11>cm^<-3> and T 1000K. 4. It has been shown that the steady magnetic field is maintained in the spiral galaxy if the effect of turbulent diffusion of magnetic fields is taken into account. 5. By computer simulations of the phenomena around a contracting magnetized cloud with rotation, the bipolar flows similar to the observed ones in the star-forming regions have been found to occur. 6. The propagation of the stellar wind from a star surrounded by a gaseous disk has been investigated intending to derive a bipolar flow. 7. It has been found by the observations of some bipolar molecular flow sources that the flow has a rotational motion and has a shell structure and the central object is accompanied with a rotating disk. 8. Twenty-one bipolar flow objects have been newly found by the survey of some star-forming regions.