Steve B. Howell, Elliott Horch, Mark Everett, and David Ciardi
High-resolution Optical Speckle
Imaging at Gemini North
A visitor instrument at Gemini North takes the highest-resolution, ground-based
optical image ever made of the Pluto-Charon system. Results have ramifications
on both the study of the not-quite-a-planet Pluto system as well as the search
for exoplanets.
“Clearly the best!” It’s the oft heard phrase
about the atmospheric clarity and seeing on
Mauna Kea, the purported first-born son of
Wākea and Papa, according to Hawaiian lore.
Well, we are here to tell you, we agree.
Mauna Kea is a premiere observing site,
especially for speckle interferometry, a
technique that employs a sequence of shortexposure “snapshots” to obtain images at
a telescope’s diffraction limit. In July 2012,
a generous allocation of Director’s time
allowed us to bring our Differential Speckle
Survey Instrument (DSSI), a speckle camera,
to Gemini North as a guest-instrument. When coupled with the superb 8-meter optics of
Gemini, that dual-channel instrument, which employs an electron multiplying CCD sensor
(EMCCD) with no readout noise, allowed our team to produce diffraction-limited shots of
Pluto and its largest moon Charon. At an angular resolution of 20 milliarcseconds (+\- 3-4
mas), these are the highest-resolution, ground-based optical images yet achieved for the
Pluto-Charon system (see Figure 1).
December2012
GeminiFocus
Figure 1.
The reconstructed
image of Pluto and
Charon obtained at
692 nm. In the image,
north is up, east is to
the left, and the image
section shown here is
1.39 x 1.39 arcseconds
across. No pixel
smoothing has been
applied to the image.
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