Master's Thesis Defense by Mette Baungaard

Title: Impact of Planetary Siblings on Terrestrial World Measurements

Abstract: Small planets are abundant in our stellar neighborhood and commonly orbit around M-dwarf stars. These stars make up 75% of our stellar neighborhood, and with the era of James Webb Space Telescope  (JWST) at our doorsteps, it is possible to characterize terrestrial exoplanets around these stars. This thesis investigates whether a planetary sibling can induce a measurable effect on the signal of a target planet observed in occultation. This thesis focuses on the exoplanet system LTT 1445A, a system of two planets orbiting an M-dwarf star. This system was chosen due to the proximity of the system to the solar system, as well as the host star being an M-dwarf, which is a cooler, smaller star and will make the signal the largest. I simulate the system using the code package starry and use the most up-to-date values for the parameters of the host star and planets. I make the simulated data in six different JWST MIRI instrument filters to see how the observational bandpass alters the observed signal. I set up the system and make simulated data and models for different planetary configurations, such as the planets containing atmospheres and situations where they do not. When defining the planets I take the extreme cases, where the incoming stellar radiation is entirely re-radiated from the sub-stellar point, creating a permanent hot spot for the no atmosphere case. For the atmosphere case, the atmosphere totally redistributes the incoming stellar radiation around the planet. I make a statistical analysis of the simulated data against a one-planet model to test if the presence of the sibling planet has a significant impact on the observations. My results show that the presence of the sibling planet has a variably significant impact on the simulated light curve depending on the orbital phase of the sibling planet, as well as its semi-major axis. There is positive evidence of significance when the sibling planet is at phases 0.3 and 0.7 for specific filters. The impact of the sibling planet increases if it is moved closer to the star. The results indicate that certain situations are significant, and one can with confidence distinguish that there is a secondary planet with no atmosphere. This is exciting as in the era of JWST, there are programs to explore these multi-planetary systems around M-dwarfs, and with the results presented in this thesis, we are bound to characterize many more exoplanets.

 Supervisors: Lars Buchhave (DTU Space, KU NBI); Hannah Diamond-Lowe (DTU Space)

 Censor: Hans Kjeldsen (AU)