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Title: The circumstellar environments of class O and class I protostars
Author: Brown, D. W.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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This study is concerned with the dynamical processes occurring during the formation of low mass stars. Observations of protostars in the Perseus and Serpens molecular clouds show evidence for outflowing gas which is used to calculate the energetics of the molecular outflows. In the case of three objects, FIRS1, SMM4 and SVS13, more detailed analysis is carried out to attempt to determine the outflow structure, and detect rotational and infall motions in the circumstellar envelopes. The effects that the angular resolution of the observations have on the results is also considered. Continuum emission from dust in circumstellar accretion discs is observed using the JCMT-CSO single baseline interferometer, enabling disc growth rates and formation timescales to be estimated. It is found that even the most deeply embedded protostars in the survey have substantial circumstellar discs, and the disc mass is not seen to significantly increase with time, placing constraints on models of disc formation and evolution. Further investigation of the kinematics in two Class I sources in the Taurus molecular cloud, TMC1 and TMC1A, clearly shows rotation in the circumstellar envelopes, permitting accurate estimates of the central stellar masses. The results confirm that these sources have accreted the bulk of their final masses, and when combined with measurements of their bolometric luminosities enables strict upper limits to the mass infall rates to be calculated. The mass infall rates differ from the rates predicted by the 'standard' model of star formation by an order of magnitude, implying that core collapse does not proceed at a constant rate during the embedded protostellar stage. Alternative models of core collapse are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available