Understanding star formation at early stages in the filamentary era

Star formation;Massive stars;Protocluster formation

Lee, I-Jen

关键词: Star formation;    Massive stars;    Protocluster formation;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/44802/I-Jen_Lee.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

This thesis presents a study of star formation at early stages in the filamentary era with a special focus on massive star and cluster formation.We first investigate the importance of filamentary structures in star formation andpropose an observationally driven scenario for the evolution of filamentary structures from large-scale molecular clouds to small-scale circumstellar envelopes.In addition, as theories of star formation have gradually shifted from individual, isolated objects to the formation of clusters over the decade, we study the environment in the protocluster IRAS 05345+3157 to better understand the initial conditions for cluster formation.With CS(2-1) observations using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) observatory, we have identified seven dense gas cores in this region and discussed the role of initial turbulence.The gas cores require an external pressure of 10^8 K cm^-3 to be bound to form possible seeds for future protostars.Furthermore, to understand massive star formation, we study the structure and kinematics of nine starless cores in Orion.As two main models about massive star formation, the turbulent core model and the competitive accretion model, predict different level of fragmentation in massive starless cores, our results from high angular resolution observations with CS(2-1) using CARMA show three to five fragments associated with each core, in a broad consistency with the models involving turbulent fragmentation.The number of fragments suggest that magnetic fields may be playing a role in suppressing the fragmentation.Also, the spectral data from the IRAM CS(2-1) observations of several cores show consistency with a picture of converging flows along a filament toward the core center; these flows may be important in massive and cluster formation.Our result does not fully support either the turbulent core scenario or the competitive accretion scenario.Finally, we present the first results from the CARMA Large Area Star Formation Survey (CLASSy) toward Serpens Main, NGC 1333, and Barnard 1.The project provides an unique opportunity to study cold, dense gas structure at millimeter wavelengths from 1500 AU to a few parsecs.The data reveal some exciting properties in morphological and kinematic structures for the first time,and will be unveiling more underlying physics in the star formation process in the future.