a “false positive.” Using this technique, the
DSSI observations at Gemini North in 2012
helped confirm over a dozen planet candi-
dates, including the five-planet system Ke-
pler-67; DSSI would eventually provide more
than 2,100 observations of Kepler planet
candidate host stars.
Based on the success of DSSI, and the need to
validate and characterize the 4,000 exoplan-
et candidates discovered to date by NASA’s
Kepler/K2 Space Telescope and the Transiting
Exoplanet Survey Satellite (TESS), Howell initi-
ated the design of two new speckle instru-
ments: ‘Alopeke and Zorro, which our team
went on to build at NASA Ames Research
Center. The twin instruments each use two
electron-multiplying CCDs and combinations
of narrow-band (40- to 50-namometer-wide)
filters to provide simultaneous two-color dif-
fraction-limited photometric and astromet-
ric information at optical wavelengths.
Each instrument can also identify back-
ground objects and companion stars — to
within < 0.1 to 1.2 arcseconds of, and up to
10 magnitudes fainter than, the exoplanet’s
host star — that can contaminate
exoplanet transit detections. For
any detected companion, speckle
imaging provides the position and
separation from the host star, as
well as color and contrast infor-
mation that greatly reduces the
likelihood of false positives and
improves the estimates of the exo-
planet size.
Zorro and ‘Alopeke:
Specifics for Users
‘Alopeke and Zorro add great new capa-
bilities, and having identical instruments
on both Gemini telescopes allows collect-
ing homogeneous datasets over the whole
sky. The speckle mode provides diffraction-
limited (0.016 arcsecond Full-Width at Half-
October 2019
Maximum at 500 nm and 0.025" at 800 nm)
resolution imaging at optical wavelengths
over a narrow field of view (~6 arcseconds).
The wide-field mode provides high-sensitiv-
ity natural-seeing imaging with virtually no
readout delay in the standard Sloan broad-
band filters over a moderate field of view
(~60 arcseconds).
Both instruments are considered "perma-
nent resident" visiting instruments, meaning
they are available throughout the
semesters for regular queue and
Fast Turnaround proposals. This
makes them great for programs
that need simultaneous photom-
etry in two filters, variability stud-
ies, and rapid events like occul-
tations, which also benefit from
the flexibility of Gemini’s queue
scheduling.
Differential Speckle Imaging
at Gemini
Some Science Highlights
Speckle image
reconstruction of Pluto
and Charon obtained
in visible light at 692
nanometers (red) with
the Gemini North
8-meter telescope using
the Differential Speckle
Survey Instrument (DSSI).
Resolution of the image is
about 20 milliarcseconds
average. This is the first
speckle reconstructed
image for Pluto and
Charon from which
astronomers obtained not
only the separation and
position angle for Charon,
but also the diameters of
the two bodies. North is
up, east is to the left, and
the image section shown
here is 1.39 arcseconds
across.
Credit: Gemini
Observatory/NSF/NASA/
AURA
Speckle imaging at Gemini Observatory is a
forefront technology allowing researchers to
push the limits of high-resolution imaging.
The following science references provide
GeminiFocus
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