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.
Multi-Object Spectrograph (GMOS) and
FLAMINGOS-2 near-infrared imaging spec-
trograph at Gemini South to survey the
southern stars in the z and J bands, respec-
tively. We also used MegaCam (an imaging
CCD camera with a 1 square degree field
of view) and WIRCam (a near infrared mo-
saic imager) at the Canada-France-Hawai‘i
Telescope to survey 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-lim-
ited observations started in 2014A and
ended in 2017B. We used the Gemini
January 2019 / 2018 Year in Review
GeminiFocus
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