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UV studies of the local interstellar medium

By David Duncan Boyce

Abstract

We present new measurements of the spatial distribution of cool and hot gas in the local\ud interstellar medium as a result of a search for O VI absorption in the FUV spectra of\ud 100 white dwarfs at distances between 50 and 300 pc. We have carried out a detailed\ud velocity analysis on the detected O VI lines to ascertain the degree of contamination from\ud the background star. The position of the stars relative to the local cavity is calculated\ud through cold gas phase column density measurements. Through curve of growth analysis\ud we note that the local cavity is depleted in metals relative to hydrogen by a factor of 5\ud -10 compared to the space beyond.\ud Whereas the O VI producing hot gas was originally thought to be observed in the interface\ud regions between hot and cold gas, i.e. the cavity wall, our investigation nds no\ud unambiguously hot gas in lines of sight that span such regions. We do, however, nd hot\ud gas at high galactic latitudes where there are no such walls. We discuss the wider context\ud of this result by comparing the position of these detections to the soft X-ray background.\ud This work ultimately changes our picture of the local interstellar environment and its\ud processes by removing the ubiquitous million degree gas that was once thought to surround\ud the solar system. One possible explanation worthy of further investigation is that\ud the local cavity has recently begun to be inundated by hot gas spilling out of the loop 1\ud supernova remnant.\ud In support of this work there is an enclosed CD that contains the data and models used in\ud this thesis. Examples of the information found on this CD can be found in the appendix.\ud Explanations of the data, charts and graphs can be found in the body of the text when\ud required

Publisher: University of Leicester
Year: 2009
OAI identifier: oai:lra.le.ac.uk:2381/7929

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