GeminiFocus January 2019 | Page 7

paved the way for astronomers to search for similar giant planets but on very wide orbits around stars. Giant planets on wide orbits are of inter- est for several reasons. They are so far away from their host that the star’s light does not affect them. This means they can be imaged and studied directly (as if they were isolated objects) without the need for sophisticated imaging and data analysis techniques. In some cases, high-resolution spectra can also be acquired to learn more about them. And because the planet and its host star formed together, they share the same age and dis- tance from Earth; thus, they are generally more interesting to study than isolated ob- jects, for which age and distance is notably more difficult to obtain. Of the 20 or so planets detected by direct imaging, about half belong to a class of giant planets whose orbits have a very large semi- major axis (greater than 100 AU); no such planet exists in our Solar System. We, there- fore, began a WEIRD (Wide-orbit Exoplanet search with InfraRed Direct imaging) survey for the most extreme planetary systems. Object Spectrograph (GMOS) and FLAMIN- GOS-2 near-infrared imaging spectrograph at Gemini South to survey the southern stars in the z and J bands, respectively. We also used MegaCam (an imaging CCD camera with a 1 square degree field of view) and WIRCam (a near infrared mosaic imager) at the Canada-France-Hawai‘i Telescope to sur- vey the northern stars in the same bands, respectively. Overall, the project required about 250 hours of ground-based observing time and an additional 250 hours of Spitzer Space Telescope / InfraRed Array Camera (IRAC) imaging at 3.6 and 4.5 microns (µm) to complete the observations. Results from the WEIRD Survey As giant planets have spectra that resemble T or Y dwarfs (with different surface gravi- ties), we employed the same strategy used by those searching for brown dwarfs with wide-field imaging. The characteristically red z-J and [3.6]-[4.5] colors of known planetary- mass companions and young brown dwarfs were the criteria used to identify candidates (Figure 1). The search uncovered four candi- date companions with the expected colors, Figure 1. Spectral energy distribution of young T to Y dwarfs. The transmission functions of the four filters used for our observations (z, J, [3.6], and [4.5]) are overlaid. The WEIRD Survey Designed to search for Jupiter-like com- panions on very wide orbits (1,000 to 5,000 AU), the WEIRD survey focuses on the 177 stars younger than 120 million years that are known members of moving groups in the solar neighborhood, closer than 70 parsecs. Unlike stars, planets do not have core nuclear reactions allowing them to sustain their temperature. Thus, after their formation, they cool down with time. A young planet will therefore be brighter than the same planet at an older age, and easier to detect directly. The data collection of deep seeing-limited observations started in 2014A and ended in 2017B. We used the Gemini Multi- January 2019 GeminiFocus 5