Tackling Magnetic Active Regions in Radial Velocities: Strategies to Improve and Expand Small Exoplanet Mass Measurements

Abstract

Several big-picture goals of exoplanet science now depend on building a population of small exoplanets that are well-characterized, having both a measured radius and a measured mass. Radii have been measured for approximately 3000 confirmed small exoplanets, mostly thanks to space-based transit detection surveys. Of those 3000 small exoplanets, fewer than 300 are well characterized. The majority of small exoplanet masses have been measure via radial velocity (RV) detection, but significant challenges to doing so are presented by RV signals inherent to activity in the host star. Magnetic active regions (ARs) on the surface of the star dominate these stellar activity signals on timescales related to the rotation period of the host star. With a plethora of modern ground-based high-resolution spectrographs, instrumental RV precision has been improved to as low as 0.3 m/s. With these improvements, RV signals associated with ARs have become the main limitation to measuring small exoplanet masses with RV detection. In this thesis, I present three studies that demonstrate novel methodologies for tackling the issue of magnetic AR signals in RVs. These methods include: a simulation strategy to characterize periodic AR signals, a seasonal technique to combat AR-induced RVs in fits, and a spectral analysis that isolates the AR-induced component of the RV signal.