Diversity of the Sub-Stellar Realm

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After millennia of speculation and a century of false starts, astronomers have found hundreds of confirmed planets and thousands more planet candidates around other stars since the mid-1990s. The pace of discovery continues to accelerate, as different (and often complementary) detection techniques mature, and as more capable ground- and space-based instruments come into play. Meanwhile, the past two decades have also witnessed the identification of a new class of astronomical objects called "brown dwarfs", which straddle the boundary between stars and planets. The two types of objects -planets and brown dwarfs- are collectively referred to as sub-stellar objects. I propose an ambitious, multi-faceted research program, using state-of-the-art instruments on several of the world's largest telescopes, to investigate the diversity of sub-stellar objects. Specifically, I propose to (1) characterize close-in transiting planets using data from the Kepler space telescope as well as innovative high-precision observations with ground-based telescopes; (2) search for and characterize sub-stellar companions of nearby young stars through high-contrast, high-angular-resolution imaging and spectroscopy; and (3) identify and characterize the lowest mass isolated brown dwarfs using deep wide-field surveys of nearby young star clusters and follow-up spectroscopy. The proposed work will not only advance our understanding of the origins, evolution and diversity of planets and brown dwarfs, but also contribute to the emerging research area of `comparative exoplanetology'.