David Pinfield, Bartek Gauza
Ultra-cool companions may be brown dwarfs or planetary mass objects, with known discoveries ranging in effective temperature from ~2700 K down to just a few hundred K. The question of how brown dwarfs and giant planets should be classified/understood is not yet answered, with a full understanding of the "exoplanet brown dwarf connection" being an important goal in the field. Ultracool companions are a crucial ingredient, providing excellent test-beds to helping astronomers understand the complex ultracool atmosphere physics at play. With the recent advent of the Gaia observatory we now have access to an unprecedented set of primary star measurements, which are providing constraints (through association) on companion properties including distance, temperature, surface gravity, mass, age and composition. In this project you will join a team working to fully exploit the powerful combination of Gaia with world-leading infrared surveys, and identify and study ultracool companion populations out to several hundred parsecs (we describe our overall programme in: https://arxiv.org/abs/1706.06038). We are specifically targeting companions with the most extreme properties, such as the youngest planetary mass objects, and the coolest brown dwarfs with temperatures down to room temperature.