Investigating star-planet properties of different exoplanet populations

Abstract

Numerous groundbreaking discoveries have been made in exoplanet science over the past decade. Recent exoplanet search surveys have provided compelling evidence that planets are exceedingly common, with the majority of stars in our Milky Way galaxy hosting one or more planets. The census has also revealed a rich diversity of exoplanetary systems and raised many fundamental and challenging questions. Answers to some of the questions would partly depend on understating the complexity of planet formation and evolution processes and accurately determining host-star and planet properties. In this thesis work, I have studied the different exoplanet populations in terms of their host-star properties and key planetary characteristics. Specifically, I have investigated the mass-metallicity relationship for directly imaged young and massive gas giant planets found at large orbital separations (> 5 AU). The metallicity scatter found in these studies indicates that the formation mechanism of gas giants at large orbital distances is different from the Jupiter analogs found in closer orbits. The age analysis of star-hosting planets, which also forms a part of this thesis, was carried out using elemental abundances, isochrone fitting, and the space velocity of stars determined from GAIA DR3. Combining various pieces of evidence, we were able to show that the formation timeline of small planets precedes the formation of giant planets. That is to say, the stars hosting giant planets are statistically younger compared to those hosting smaller planets. Furthermore, these results are shown to be consistent with planet formation by the core-accretion process and galactic chemical evolution. Finally, using high-contrast imaging data from SPHERE/VLT, I studied the young ( ∼ 3 Myr old) planetary system Lkca 15 and modeled the properties of dust grains and the morphology of the protoplanetary disk in this system with the goal of understanding the influence of grain properties (size and composition) on the formation of giant planets on such short timescales.