Exoplanet Detection around M Dwarfs with Near Infrared and Visible Spectroscopy

In recent years, exoplanet science has begun to focus on M-dwarf stars as highly interesting targets for exoplanet detection and characterisation. The reasons for this are multiple: M dwarfs are the most common stars in the galaxy; their small size means smaller exoplanets can be detected than around G-type stars; the liquid-water habitable zone is closer to the star, hence these planets are faster and easier to detect. The emerging population of planets hosted by M dwarfs shows intriguing characteristics compared to planets hosted by FGK stars, such as a lack of hot Jupiters, and an uncertain planet metallicity correlation. The aim of this thesis is to explore the detection of exoplanets around M dwarfs via the radial velocity method, in both the near infrared and visible domains. I also carried out a statistical analysis of the known population of planets around M dwarfs, as it stood both at the start of the thesis and at its conclusion. In the visible, I worked with the SOPHIE spectrograph at the Observatoire de Haute- Provence, as part of the SOPHIE exoplanets consortium. This group, which nucleates researchers in multiple institutes in France and neighbouring countries, has been carrying out several long-term exoplanet surveys, one of which focuses on the search for planets around M dwarfs (with special attention to Neptunes and super-Earths). I applied a template-matching algorithm to the targets of this subprogram, and analysed the resulting radial velocity time series. Through this analysis, I was able to confirm the significance of periodic signals that, while apparent in the traditional CCF analysis, were partially hidden by noise. I also studied a variety of stellar activity indicators, identifying those most suited to SOPHIE spectra. The first four exoplanets from this subprogram have recently been published; I was lead author for two of the three papers. In the near infrared, I worked with the SPIRou spectropolarimeter at the Canada France Hawaii Telescope, as part of the SPIRou consortium. This new instrument was conceived specifically for the observation of M dwarfs, which are faint in the visible and emit most of their radiation in the infrared. I worked on the development of the data reduction pipeline, with specific focus on the wavelength solution - that is, the correspondence between pixel position and wavelength, which is crucial to the measurement of precise radial velocities. I developed and tested ways to combine different wavelength calibrators, for an accurate wavelength solution. (author)