Spectro-astrometry as a Tool for Detecting Planets in Transitional Disks
The goal of understanding how our solar system formed has been a long standing one. We have already answered the question \is our solar system unique?" by detecting an ever-growing population of extra solar planets orbiting stars of many different sizes and temperatures. It is much easier to detect a large planet that orbits close to its star as opposed to a smaller, more distant one. This led to the discovery of many Hot-Jupiters in the initial stages of exoplanet detection, but increased efficiency in both ground and space-based detection techniques expanded the catalogue of exoplanets to include a truly diverse range. In order to understand how these planets are formed we need to investigate planet formation in the earliest stages. Traditional techniques like transit photometry and the RV method are difficult to apply to these objects due to their instability, and direct imaging remains difficult to perform. Here we investigate the possibility of using spectro-astrometry to detect planets around young stars. UVES spectra of T Cha were obtained with a spectro-astrometric study in mind, and the technique is also tested by applying it to UVES spectra of HD 142527, a young Herbig Ae/Be star with a known brown dwarf companion. Chapter 1 covers an introduction into the topic of star and planet formation, and describes the specific type of star this project intends to probe: Transitional disk objects. The main four exoplanet detection techniques currently in use are described, and a discussion of whether they can be used for detection of exoplanets still in formation accompanies each. Chapter 2 then describes the technique of spectro-astrometry as it has been used before. We also look into some of the advantages and disadvantages of using it and how the problem of planet detection around young stars could be overcome via spectro-astrometric analysis. In Chapter 3, details of the instrument used for our observations is provided. A description and discussion of the data reduction process then follows. Several artefacts that were found in the course of this project are also analysed. Chapter 4 covers results of our analysis on the T Tauri variable type star, T Chamaeleontis. The aim of the study is to determine if it is possible to accurately detect the Hx emission from the hypothesised exoplanet T Chamaeleontis b. No detection was proven, but limits are placed on the _M acc of the exoplanet and the detection limit using spectro-astrometry. In Chapter 5, a bridge between binary detection (of which spectro-astrometry is well established) and exoplanet detection (of which has not been proven) is presented in the analysis of HD 142527. HD 142527 is orbited by a 0.13 Mx Very Low-Mass star, which is around 100 times larger than the expected size of T Chamaeleontis b. Evidence for a detection is presented and finally discussed. Chapter 6 summarises all results and conclusions that were found throughout this thesis, and a discussion on the efficacy of spectro-astrometry as a detection technique for exoplanets around YSOs.
National University of Ireland - Maynooth
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