trometry to at least the 0.9 maslevel in a 3-minute observation and
provide a photometric measurement of the stars observed to +/0.1 magnitude at Gemini North.
bital dynamics of this pair for the 2015 encounter by NASA’s New Horizons spacecraft.
DSSI: The Instrument
The DSSI consists of an optics box that contains the field lens, beam splitter, and filters.
It simultaneously sends the light to two iXon
EMCCD cameras. The filters and beam splitter
are changeable, and due to their small size,
relatively inexpensive. A PC based software
program runs both the
instrument and the two
cameras. Typically, we observe in the visual through
infrared bands, although
any optical band is possible, being constrained
only by the CCD quantum
efficiency profile.
We have used our speckle camera
in a broad survey of exoplanet
candidate host stars employing
the WIYN telescope in Arizona
and now Gemini North. At WIYN
we examined the bright star
sample and used Gemini North
for a more selective program
aimed at the smallest, Earth-like
exoplanet candidates orbiting within their
habitable zones.
Figure 3 shows a summary of our typical observations at the two telescopes. Gemini
North provides higher resolution (i.e., closer-in views near the target star) and deeper
limiting magnitudes; Gemini’s superior
telescope size, optics, and high-altitude
location also allows us to observe fainter
target stars than at WIYN. While our engi-
Speckle data are obtained
through very narrow band
(~40 nanometers) filters
centered on the wavelength of interest. EMCCD
readout generally consists
of a windowed sub-region,
covering 2-3 arcseconds
on a side at a plate scale of
~0.01 arcsecond per pixel.
DSSI can also perform as-
December2012
Figure 3.
Summary of the Geminilimiting magnitude at
0.2 arcsecond and the
target brightness we can
reach with our speckle
camera. Filled circles are
the results at 692 nm,
and open circles are the
results at 880 nm. The
boxed points are cases
where results from two
nights were combined.
The shaded area marks
the region of most points
in the same plot for
WIYN telescope data. All
points are marked at the
estimated 5-sigma limit
at a separation of 0.2
arcsecond. Doubling the
observation time would
move points upward by
0.25 magnitude, and
if 3-sigma limits are
desired, all points would
move upward by 0.55
magnitude.
Figure 4.
The reconstructed image
of the Pluto-Charon
system with their
angular sizes drawn
(dotted circles inside
“glare”) along with the
angular sizes of four
known stars. Note that
our imaging system on
Gemini can also resolve
the largest stars.
GeminiFocus
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