PhD Defense: Pia Cortés Zuleta

Abstract:

M dwarfs have become favorite targets for exoplanet detection and characterization. Their low mass makes them ideal to perform radial velocity (RV) surveys since, for a given planet’s mass, the planet’s gravitational pull will be greater than for Sun-like stars. However, M dwarfs are known to be magnetically active stars. Stellar activity is currently one of the main limitations to detecting low-mass planets as it induces quasi-periodic RV variations of the order of a few meters per second. This thesis aims to characterize and study the stellar activity of M dwarfs using high-precision spectroscopy in the optical and near-infrared (nIR) domains to improve the detection of low-mass planets. In the near-infrared domain, I used high-precision spectroscopy and spectropolarimetry from SPIRou, which is mounted at the Canada-France-Hawaii telescope. The computation of the precise radial velocity is challenging in the near-infrared due to the high amount of telluric lines in their spectra. On the one hand, I worked closely with the Data Reduction System team and performed several tests to measure the impact of the mask selection in the CCF computation. On the other, I developed computational tools to obtain activity indicators from SPIRou spectra based on the CCF shape and on the pseudo-equivalent width of spectral lines in the SPIRou domain. I tested their performances in a sample of M dwarfs. In the optical domain, I worked with the SOPHIE spectrograph located at the Observatoire de Haute Provence. A dozen of SP3 targets are being monitored quasi-simultaneously with SOPHIE and SPIRou to improve the characterization of the stellar activity jitter in the optical and near-infrared. I used the template-matching algorithm NAIRA to compute the SOPHIE RVs and activity indicators of the SP3 targets. I led the first publication of a SOPHIE+SPIRou target, the early M dwarf Gl 205, on which I performed an extensive analysis of the stellar activity signal in both domains using the data-driven technique of Gaussian Processes. I analyzed the RVs and activity indicators of the SOPHIE+SPIRou complete sample to look for periodicities related to stellar activity and planets. I identified two interesting targets with compatible signals in the optical and NIR. A second publication is under preparation with a detailed analysis of the stellar activity and one possible Keplerian.