Awad, Z.M.A.-H.; (2010) The chemistry of warm cores in low-mass star forming regions. Doctoral thesis , UCL (University College London).

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Abstract

My thesis deals with the investigation of the chemical and physical properties of the gas and dust involved in the formation of low mass stars. As the stars form, warm cores (or ‘hot corinos’) are detected in molecular emission. The study of such emissions allows us to get an insight on the physical conditions of low-mass star formation, and trace its various evolutionary stages. Through out this thesis I make use of a chemical model originally developed for the study of high mass star forming regions. I have adapted this model for the study of low mass stars and first applied it to explore the sensitivity of the chemistry of hot corinos to the changes in the physical conditions of the surrounding environment. It is found that the chemical trends of these cores does not qualitatively differ much from that of hot cores (remnant of high mass star formation) leading us to conclude that, at least in some cases, the formation of low-mass stars may be a scaled-down version of that of massive stars. One of the most studied hot corinos is that surrounding IRAS 16293-2422: in order to validate my model, I compare the predicted chemical abundances to the molecular emission from this object and find a relatively good match. Observations of warm cores also revealed that they are rich in deuterium content. I enlarge our chemical network to include all the possible mono-deuterated species, as well as D2CO. In this study, I look into the chemical evolution of the deuterated species, and aim to identify a set of deuterated molecules as evolutionary indicators for the protostellar stage of the core. A very debated issue when validating chemical models is that of whether the initial chemical conditions of the gas affect the chemical evolution of the star forming cores. I investigate this issue by running a large grid of dark and dense cloud models where the initial conditions are varied, in particular I investigate whether a pre-processed gas (e.g. ‘left over’ from a previous star formation event) may affect subsequent star formation processes and find that in general the initial chemical composition of the gas is in fact irrelevant. Finally, I took part of a study, led by Dr Bayet, where the chemistry of deuterated species in extragalactic environments is investigated and in this thesis I highlight my contribution to this work.

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