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The physical and chemical evolution of star forming regions

Ruffle, Deborah Patricia; (1998) The physical and chemical evolution of star forming regions. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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A wide variety of molecular species are observed in regions of star formation. The chemistry is measured to change between different sources; analysis of these observed chemical changes provides a probe of the physical and chemical mechanisms occurring within different regions. Of particular importance is the gas-dust interaction, which affects the physical and chemical properties of interstellar gas. In this thesis, theoretical models of the physics and chemistry in star forming regions are applied to existing observational data, in attempts to deduce the evolutionary history and physical conditions of such regions. In some cases, the models are used to suggest other species that could be observed to further explore the dominant mechanisms occurring in different regions. An investigation into the initial support and collapse of diffuse clumps to form dense cores suggests that a clump may require a minimum column density for star formation to occur. For the first time the chemical evolution of a cloud that is initially magnetically supported against collapse perpendicular to the field lines, but is collapsing along the field lines, up to an unknown but critical density is explored. It is shown that observations may reveal the value of the critical density. Study is made of the gas-dust interaction. Some molecular species which have been used as signposts of cloud evolution are demonstrated to be indicative of both early and late times; implications of this are discussed. The sulphur depletion problem is explored; a simple model is suggested where S+ is accreted rapidly onto dust grains. In addition, the elemental depletions in star-forming cores are examined with reference to the use of species to search for signatures of infall. Finally, it is established that low temperature homonuclear diatomic molecules, which are thought to be unobservable, should be detectable in cold interstellar clouds.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The physical and chemical evolution of star forming regions
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Pure sciences; Star formation
URI: https://discovery.ucl.ac.uk/id/eprint/10097532
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