`OHANA to Link Seven Mauna Kea Telescopes (Forwarded)

W.M. Keck Observatory
Kamuela, Hawaii

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Laura K. Kraft
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January 13, 2006

`OHANA to Link Seven Mauna Kea Telescopes

MAUNA KEA, Hawaii -- A team of scientists in partnership with the W. M.
Keck Observatory in Hawaii have successfully passed the first test in a
project that will link the seven largest telescopes on Mauna Kea together
to create a gigantic imaging instrument nearly one half mile (800 meters)
in diameter. The `OHANA (Optical Hawaiian Array for Nanoradian Astronomy)
array, or "interferometer," will provide ultra-high resolution images of
the near-infrared universe, 80 times more accurate than a single 10-meter
Keck telescope. The results of the first successful test between the two
Keck telescopes are described in the January 13th issue of Science.

An interferometer is a type of instrument that combines light from two or
more telescopes to obtain measurements with higher resolution than what
could be obtained with a single telescope alone. With conventional
telescopes, the size of a single, primary mirror will determine its
ability to resolve small-scale structure on the sky. But with an
interferometer, the distance between the telescopes, or "baseline," will
determine the angular resolution.

"The next large telescopes will certainly be 30 to 50 meters in diameter,
when some of the answers we are looking for would require mile-long
diameters. Only interferometers can achieve this; and the Mauna Kea summit
is the only place where we can find large optical telescopes spread over
such distances," said Dr. Fred Chaffee, director of the W. M. Keck
Observatory.

The `OHANA project, named after the Hawaiian word for family and extended
family, will eventually link the Subaru Telescope, NASA Infrared
Telescope, Gemini Observatory, Canada-France-Hawaii Telescope, the United
Kingdom Infrared Telescope Facility and the Keck I and Keck II telescopes
together with "single-mode" optical fibers never used before to transport
the light between telescopes.

"The use of fibers to transport the light between telescopes is one of the
main challenges of the `OHANA project," said Dr. Olivier Lai, resident
astronomer at the Canada-France-Hawaii Telescope.

When complete, `OHANA will be the most highest-resolution, near-infrared
instrument in the world -- capable of producing images with an
unprecedented resolution of 0.5 milliarcseconds, about the size of an edge
of paper as seen from one hundred miles away. It will be used to take
detailed images of stellar surfaces, giant gas planets, long-period
variable stars and significantly advance the understanding of stellar
astrophysics.

Modern interferometers typically have baselines a few hundred yards in
distance. Increasing the distance (and its corresponding resolving power)
usually requires a large number of mirrors, each of which deteriorates the
quality of light arriving at the detector for measurement. A solution to
this problem may be single-mode optical fibers which transmit light only
at a particular wavelength of interest and significantly reduce the loss
of light over large distances. The first experiment of the `OHANA project
was to test the effectiveness of these types of fibers and to determine
the feasibility of using them with long baseline optical interferometers.

The first `OHANA test was conducted on June 17 with the Keck I and Keck II
telescopes. Both telescopes guided on a relatively bright star (107
Hercules), located 278 light years away. The single-mode fibers were used
to transmit the infrared light over a simulated baseline of ~550 yards
(~500 meters), which was then coherently combined and successfully
measured. The experiment was the first major milestone for the future of
very large optical arrays connected with optical fibers.

"This first success is not only important for `OHANA but also a major
milestone towards future kilometric arrays of telescopes in the near
infrared," said Dr. Guy Perrin, astronomer at Paris Observatory.

Future tests will link the Canada-France-Hawaii Telescope with the Gemini
North telescope, followed by other baselines such as Subaru Telescope to
W. M. Keck Observatory for example. The goal of each test is to
characterize the baseline between telescopes before completing the entire
Mauna Kea array.

A unique aspect of the `OHANA project is its non-invasive approach for
expanding the capabilities of the existing facilities at Mauna Kea. In
response to community concerns, many scientists at Mauna Kea are seeking
ways to efficiently use the existing world-class telescopes in creative
new ways. The `OHANA project will not require the construction of any new
permanent facilities, and the very thin optical fibers used to connect the
telescopes can be installed using the existing roads and infrastructure of
the Astronomy Precinct.

"`OHANA demonstrates the spirit of cooperation between the observatories
on Mauna Kea to make the best use of the existing research resources
whenever possible," said Dr. Rolf Kudritzski, director for the Institute
for Astronomy at the University of Hawaii, which manages the astronomy
research program at Mauna Kea. "The `OHANA Project uses the best of what
we have to combine the power of the largest telescopes in the world to
create a unique new astronomical facility of unprecedented capability.
This is a milestone for the future of astronomy on Mauna Kea."

The `OHANA project is led by Paris Observatory in collaboration among
Canada-France-Hawaii Telescope Corporation, W.M. Keck Observatory, the
National Astronomical Observatory of Japan, Gemini Observatory, United
Kingdom Infrared Telescope, NASA Infrared Telescope Facility, the
Institute for Astronomy at the University of Hawaii, the National Optical
Astronomical Observatory, the, Institut National de Rercherche en
Communication Optique et Micro-Ondes and Institut National des Sciences de
l¹Univers du CNRS.

The W. M. Keck Observatory is operated by the California Association for
Research in Astronomy (CARA), a non-profit 501 (c) (3) corporation whose
board of directors includes representatives from the California Institute
of Technology, the University of California, and the National Aeronautics
and Space Administration.

IMAGE CAPTIONS:

[Image 1:
http://keckobservatory.org/news/scie...ohana/fig1.png (947KB)]
Routing of single-mode fibers from the Keck Nasmyth foci down to the
basement beam combination laboratory. Fibers are attached to the telescope
structure like regular cables and go through the cable wrap system to
prevent any damage when the telescopes rotate in azimuth. The remaining
fiber lengths (approximately 200 m for each arm) are wrapped on spools in
the basement.

Image credit: W. M. Keck Observatory/`OHANA

[Image 2:
http://keckobservatory.org/news/scie...ohana/fig2.png (507KB)]
Sketch of the interfacing of the `OHANA fibers output with the Keck
Interferometer delay lines and beam combiner.

Only one beam/fiber is shown for the sake of clarity. The two beams follow
equivalent paths. The fiber is placed at the focus of an off-axis parabola
(OAP) to produce a collimated beam. The beam is reflected with a flat
mirror (M10) towards the Long Delay Line. It is then launched into the
Fast Delay Line. The beam size is reduced in a Beam Compressor and feeds
the Beam Combiner.

Image credit: W. M. Keck Observatory/`OHANA