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Title: The chemical evolution of low mass prestellar cores and young stellar objects
Author: Roberts, Julia Florence
ISNI:       0000 0004 2671 4749
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2008
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In this thesis we develop models of the chemical kinetics of prestellar cores, so we can identify molecules which will be able to trace various physical processes, and therefore give us more understanding of how stars form from these objects. First, we investigate non-thermal desorption mechanisms which can operate inside prestellar cores, and make estimates of the desorption efficiencies based on observational data, which before now were poorly constrained by theory. We then use our chemical models to predict molecular abundances during the collapse phase of a prestellar core. In particular we investigate the effect of different initial conditions and collapse models, so we can identify molecules which could be used to distinguish between slow and rapid star formation models. We also generate line profiles for selected molecules using a radiative transfer code, using the abundances predicted from our chemical models. We find that for CS, a double peaked line profile with a blue asymmetry can only be produced for models of core collapse with extended inward motions. This contradicts many previous interpretations of line profiles, which have explained the infall signature by collapse models with a static envelope and temperature gradient. We also explore deuterium chemistry in prestellar cores, to investigate whether core collapse by ambipolar diffusion can leave a signature on deuterium fractionation. We find that the fractionation is very sensitive to the density profile of the core, thus we propose that observations of the spatial distribution of deuterated molecules could be used to distinguish between different collapse models. Finally, we investigate the chemistry in C-shock regions associated with outflows of young stellar objects, where we also include the analysis of some new observations of outflow LI448mm, which show very strong evidence for the presence of a magnetic precursor.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available