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.
