A Window into the Cradle of Planets : Direct detection and characterisation of young sub-stellar objects using high-contrast tools

Ever since we first laid eyes on the twinkling lights in the night sky, our species began its age-old quest to understand how we came into existence as a planet and what the future holds for it. Most of the traditional formation theories of planets were anchored on the examples drawn from our own solar system. With the surprising and emerging trends among the yet incomplete exoplanet demographics, we are at the wake of a rigorous revision of our theoretical understanding of how planets form and evolve. To form accurate theories however, it is necessary to base them on a planet population that spans the complete range of parameter space not only in terms of its physical properties like mass and orbital separation, but also with respect to the type of stars that host these planets and their age. In this regard, direct detection, whereby you measure photons coming from the planet, helps one get closer to the whole picture since the ideal target population for this technique are young, giant planets in wide orbits that are generally difficult to observe with other detection techniques. Over the last few years, the sensitivity reached by direct imaging observations has seen tremendous improvement owing to the use of high-contrast tools like coronagraphy and adaptive optics. The development of high-resolution spectrographs together with advanced post-processing techniques have recently, for the first time, enabled witnessing planets while in the process of being born, helping us understand how they grow by devouring material from the planetary nursery — a mechanism known as accretion. This is an exciting era for planetary science, with many ongoing as well as planned future surveys with both ground and space-based telescopes dedicated to unravelling the mysteries surrounding the origin of planets. In this thesis, I provide an overview of direct detection as a tool to study sub-stellar objects – a categorisation that includes both planets and brown dwarfs, and whose blurr