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
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