Detection and Analysis of Debris Discs

Marshall, Jonathan Peter (2011). Detection and Analysis of Debris Discs. PhD thesis The Open University.



Debris discs are the dusty remnants of the planet formation process around main sequence stars, detected through their emission at infrared wavelengths. The study of these objects improves our understanding of both the frequency and the timescale of planet formation around other stars, and, in resolved disc systems, can be used as an indirect method of planet detection in regions of orbital radius-planet mass space where standard methods (e.g. radial velocity, transits) are insensitive.

In Chapter 1, an overview of debris discs is presented, summarising the key results since their discovery and a synopsis of the most recent results. The motivation and goals for the research undertaken in this thesis are also placed within the context of our current understanding of debris discs. In Chapter 2, the mathematics of the computer models used in fitting debris disc observations with physical structure and dust grain properties are explained, starting from the black body approximation.

In Chapter 3, a search for new YSO candidates in the LI551 region is presented, comparing the YSO population with both the Taurus cloud and other similar low mass star forming regions.

In Chapter 4, the results of a search for debris discs in the AKARI FIS all sky survey are presented. Over 50 debris disc candidates are identified in the survey, though half of these have been previously observed by IRAS. Two dozen new candidates are identified at 90 μm.

In Chapter 5, a search for mid infrared excess from DUNES sources in the AKARI IRC point source catalogue is presented. Fourteen stars with infrared excess are identified, from the 102 stars with 18 μm photometry in the 133 star sample.

In Chapter 6, the Herschel ATLAS field observed during the science demonstration phase is analysed, looking for debris discs at sub-mm wavelengths. The surprising result indicates the presence of several very high mass discs (> M), with no reported excess in the far infrared, implying these discs are widely separated from their stars and very cold.

In Chapter 7, a dynamical study of the HR8799 planetary system is presented, using the MERCURY code to test the stability of the observed planetary architecture over Myr timescales. From these simulations, the influence of planetary eccentricity on the system is determined, and a comparison made to previous dynamical models of the planets.

In Chapters 8 and 9, the main findings and conclusions of the thesis are summarised and discussed. A short section giving details of the current and near-future work being undertaken on the basis of this thesis is also provided.

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