1,057 research outputs found

    Mathesis of star formation – from kpc to parsec scales

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    In this thesis I present a series of studies aiming to understand the formation of stars from gas in the Milky Way. Generally speaking, I will progress from larger to smaller scales. The kilo-parsec scale (1000 parsec ~ 10^21 cm) is the scale at which dynamics of the molecular clouds is coupled to dynamics of the Milky Way disk. Here we present an observational study of molecular gas at 49.5 deg Molecular clouds (1 - 100 parsec) are the nurseries of the stars. There are many indications that molecular clouds are turbulence-dominated objects. However, it is not clear what role gravity plays. We propose a new method (G-virial) to quantify the role of gravity in molecular clouds. Our new method takes the gravitational interactions between all pixels in 3D position-position-velocity data cube into account, and generates maps of the importance of gravity in 3D position-position-velocity space. With our method we demonstrate that gravity plays an importance role in the individual regions in the Perseus and Ophiuchus molecular cloud, and find that high values of G-virial are reached in cluster-bearing regions. We also demonstrate the capability of our method in finding regions and quantifying the properties of the regions in the clouds. Protostellar outflow ~ 1 pc is a prominent process accompanying the formation of stars. In this work, we theoretically investigate the possibility that the outflow results from interaction between the wind and the ambient gas in the form of turbulent entrainment. In our model, the ram-pressure of the wind balances the turbulent ram-pressure of the ambient gas, and the outflow consists of the ambient gas entrained by the wind. We demonstrate that the outflow phenomena can be naturally generated through this process, and discuss the potential usage of outflows as a probes of the dynamical state of the turbulent molecular gas

    A 500 pc filamentary gas wisp in the disk of the Milky Way

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    Star formation occurs in molecular gas. In previous studies, the structure of the molecular gas has been studied in terms of molecular clouds, but has been overlooked beyond the cloud scale. We present an observational study of the molecular gas at 49.5 degree <l<52.5 degree and -5.0 km/s <v_lsr <17.4 km/s. The molecular gas is found in the form of a huge (>= 500 pc) filamentary gas wisp. This has a large physical extent and a velocity dispersion of ~5 km/s. The eastern part of the filamentary gas wisp is located ~130 pc above the Galactic disk (which corresponds to 1.5-4 e-folding scale-heights), and the total mass of the gas wisp is >= 1 X 10^5 M_sun. It is composed of two molecular clouds and an expanding bubble. The velocity structure of the gas wisp can be explained as a smooth quiescent component disturbed by the expansion of a bubble. That the length of the gas wisp exceeds by much the thickness of the molecular disk of the Milky Way is consistent with the cloud-formation scenario in which the gas is cold prior to the formation of molecular clouds. Star formation in the filamentary gas wisp occurs at the edge of a bubble (G52L nebula), which is consistent with some models of triggered star formation.Comment: Accepted for publication in A&

    Differential quadrature solutions to dynamic response of cylindrical shell subjected to thermal shock

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    The dynamic response of the cylindrical shell subjected to thermal shock is investigated. Based on the classical shell theory, dynamic governing equations of thin shell with the simply supported edges under thermal shock are derived by using Hamilton principle. The temperature field, the thermal axial force and the thermal bending moment are obtained in combination of Laplace transform and series expansion when the internal surface of shell is subjected to thermal shock loading. Considering of the axisymmetric deformation, the transient displacements and thermal stresses of the shell are obtained using the differential quadrature method. The effects of the thermal shock load and the geometrical parameters of the cylindrical shell on the central deflection, the axial displacement, the bending configurations and the transient thermal stresses are analyzed
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