the ability of high-resolution
imaging with large telescopes
like Gemini, not only to assess
which stars with planets are in
binaries, but also robustly de-
termine which of the stars the
exoplanet orbits.
The Rise and Promise
of Speckle Imaging at
Gemini
The ‘Alopeke/Zorro team
preparing for instrument
installation.
Credit: Alison Peck
of innovation and crafty approaches to prob-
lems with only a fraction of the resources
necessary for most 8-meter-class telescope
instruments.
The power of these instruments was demon-
strated when Howell and his team used ‘Alo-
peke to probe the Kepler-13AB system. ‘Alo-
peke sharply resolved the two stars (Kepler
A and B), and captured a clear drop in the
light from Kepler A, proving that the planet
orbits the brighter of the two stars. More-
over, as ‘Alopeke simultaneously provides
data at both red and blue wavelengths, the
researchers could see that the dip in the
star’s blue light was about twice as deep as
the dip seen in red light.
As a very extended atmosphere would more
effectively block light at blue wavelengths,
the researchers characterize Kepler-13b as
a Jupiter-like gas-giant exoplanet with a
“puffed up” atmosphere due to exposure to
the tremendous radiation from its host star;
Thus, these multi-color speckle observations
give us a first tantalizing glimpse into the ap-
pearance of this distant world orbiting a star
in a binary system — something we know
very little about.
Our work with Kepler-13b stands as a model
for future research on exoplanets in multiple
star systems. The observations highlight
8
GeminiFocus
Speckle imaging at Gemini be-
gan in 2012 when the Differen-
tial Speckle Survey Instrument
(DSSI; designed by Elliott Horch) came to the
Observatory as a visiting instrument. This
precursor to ‘Alopeke and Zorro was grant-
ed 10 hours on Gemini North to observe
high-priority planet candidates from NASA’s
(now-retired) Kepler mission, whose prime
objective was to explore the structure and
diversity of exoplanetary systems, including
estimating how many planets there are in
multiple-star systems.
To search for planets around other stars, the
Kepler Space Telescope would stare at thou-
sands of stars and look for a slight decrease
in brightness, indicating that a planet had
transited (crossed in front of ) the star as
viewed from Earth. While the transit method
is very successful at finding planets, other
phenomena can mimic the signature of a
planet. Because of this, other methods must
be used to confirm whether a planet caused
the star’s dimming.
High-resolution speckle imaging enables as-
tronomers to not only resolve other objects
near the star hosting the planet candidate,
but detect or rule out other, non-planetary
objects that can cause a star’s light to dim
(speckle cannot see planets). This is achieved
by employing statistical techniques to as-
sess whether the observed dimming is likely
to be a true transit by an orbiting planet or
October 2019