Mitigating Stellar Activity in Radial Velocity Analyses to Determine the Physical Parameters of Six Exoplanet Systems
Large transit surveys have shown that small planets are abundant. The compositions of these planets are of particular interest as they span the transition between small rocky planets (super-Earths) and intermediate-sized planets with volatile envelopes (sub-Neptunes). The limiting factor on measuring small exoplanet masses to inform composition or atmospheric models is stellar activity. Gaussian processes are one such way to mitigate stellar activity and achieve precise planet masses. In this dissertation, we find Gaussian processes are an effective way to model solar activity and determine the solar rotation period. Our concurrent solar photometry and radial velocity analyses produce consistent results; stellar photometry may assist radial velocity activity analyses. Subsequently, we perform radial velocity analyses on six exoplanet systems hosting eleven transiting planets: K2-291, GJ 3470, K2-3, HD97658, GJ 9827, and HD 106315. We examine the stellar activity present and use a Gaussian process where relevant. With our measured masses, we comment on the potential compositions and compare these planets with other similar exoplanet systems.The eleven planets measured in this work are consistent with the theory that planets smaller than the radius valley are primarily rocky and those larger than the radius valley contain a volatile envelope.