GeminiFocus January 2019 - Page 6

Frédérique Baron, Étienne Artigau, and David Lafrenière A Hunt for WEIRD Planets The WEIRD (Wide-orbit Exoplanet search with InfraRed Direct imaging) survey was designed to search for Jupiter-like companions on very wide orbits around young stars in the solar neighborhood. Using observations from Gemini-S, CFHT, and Spitzer, the survey should have enabled the discovery and direct imaging of five to eight such new planets, but none were to be seen. Our results constrain the occurrence of 1-13 M Jup planetary-mass companions on orbits with a semi-major axis between 1,000 and 5,000 AU at less than 0.03, with a 95% confidence level. In the last two decades, the nearly 4,000 exoplanets discovered to date have come in all sizes and compositions, appearing quite different from the planets in our Solar System. Most of these planets were discovered using indirect methods, meaning that astronomers measure the effect that the planet has on its host star, while the planet itself is not seen; these indirect methods are only sensitive to planets at a few astronomical units (AU) from their star or closer. Relatively little is known for planets on wider orbits. The Interest in Giant Planets on Wide Orbits Direct imaging of exoplanets is extremely challenging. A star is so much brighter than a planet that, at very close angular separations, the emission from a planet can be easily drowned out by the light coming from its host star. Direct imaging is possible, however, with state-of-the-art high contrast imagers (such as the Gemini Planet Imager) that sup- presses the starlight and enables the detection of companions as close as 10-20 AU. In 2004, the European Southern Observatory’s Very Large Telescope Array made the first di- rect image of a planet four times more massive than Jupiter orbiting close to the nearby brown dwarf 2MASSW J1207334-393254. As a brown dwarf’s light is far less intense than that of a true star — thus making a planet orbiting it easier to detect — this discovery 4 GeminiFocus January 2019