Application d'une technique d'autocorrélation à divers domaines de l'astrophysique
|Advisor:||Borra, Ermanno F.|
|Abstract:||In this PhD project, we apply an analysis technique based on the autocorrelation function to three different fields in order to detect with great precision variations caused by different physical phenomena in the profile of the absorption lines of stellar spectra. The first subject relates to the measurement of stellar magnetic fields. We obtained the variation curve of the mean magnetic field modulus of 18 stars as a function of their rotation period and compared some magnetic curves obtained with the autocorrelation technique with those of another research group who used a conventional method. For all cases, the autocorrelation technique gave us magnetic curves of a higher precision compared to the competitive technique. The second subject that we studied pertains to the measurements of the microturbulence velocity of Cepheids with the autocorrelation technique. We obtained microturbulence curves as a function of the pulsation phase of six Cepheids. For the vast majority of the cases studied, we measured a microturbulence velocity peak at the precise moment during which the Cepheid reaches its minimum radius. These results are in agreement with previous work done on the subject. The third and last subject refers to the detection of exoplanet signals by reflected light of the host star. In the visible spectrum, the signal of a planet is approximately a copy of that of its host star but of much lower intensity (i.e. 10-⁵ à 10-⁴ the intensity of the star). As a result, detecting the planetary signal in the visible band with an acceptable degree of certainty is a major challenge. For this portion of the project, we have highlighted the advantages of the autocorrelation function compared to an already well-established method in astrophysics based on the cross-correlation function using simulated spectra. In addition, we analyzed the 51 Peg + 51 Peg b planetary system. We succeeded to measure the 51 Peg b planetary signal with a maximum detection of 5.52 o noise. This is about 50 % higher than what was achieved by another research group using the same spectra and a cross-correlation technique.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||9 March 2020|
|Collection:||Thèses et mémoires|
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