`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 l’Univers 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