Laser Vision Gives New Eyes To Keck Telescope

http://www2.keck.hawaii.edu/news/science_mtg/gc.html

LASER VISION GIVES NEW EYES TO KECK TELESCOPE
W.M. Keck Observatory
September 17, 2004

MAUNA KEA - The Laser Guide Star Adaptive Optics system
at the W. M. Keck Observatory is exceeding performance expectations and
is poised to revolutionize many fields of astronomy. The new guide star
system, the only one of its kind on a very large telescope, allows
astronomers to use adaptive optics to study astronomical objects with
unprecedented resolution anywhere in the night sky. The system also
opens the door to wide-field imaging with adaptive optics.

"We are just thunderstruck with this new capability," said Dr. Frederic
Chaffee, director of the W. M. Keck Observatory in Hawaii. "Laser guide
stars on large telescopes are a remarkable breakthrough for ground-based
astronomy and we look forward to providing this astonishing capability
to Keck astronomers as quickly as possible."

The dramatic boost in telescope performance is due to a new laser system
that allows adaptive optics (AO) to make precise atmospheric corrections
to a scientific target. Before the laser guide star (LGS) system, Keck
astronomers had to rely on the availability of a relatively bright,
naturally-occurring star to measure and correct for atmospheric
distortions. However, such relatively bright stars are available in only
about one percent of the sky. The new astronomical laser removes these
limitations and gives almost full access to the sky for study with
adaptive optics.

"It is a tremendous achievement to turn one of the most technically
complex prototypes in astronomy into a facility-class instrument on an
operational telescope," said Dr. Peter Wizinowich, head of the Adaptive
Optics group at the W. M. Keck Observatory. "It is a significant
accomplishment for the team."

Image blurring has plagued astronomy since the invention of the
telescope nearly 400 years ago and has prevented ground-based
astronomers from studying structural details of faint objects such as
spiral arms in distant old galaxies.

"Telescopes in space and on the ground have analyzed the light from
galaxies for years, but now we can actually see the structure and
stellar population inside those galaxies," said Dr. David Le Mignant,
instrument scientist for the adaptive optics system at the W. M. Keck
Observatory. "It is as if the Keck telescope were in space!"

With the atmospheric blurring removed by the Keck adaptive optics
system, and the large diameter of a 10-meter mirror, the Keck II
telescope is now more powerful than even the largest space-based
telescope for looking at the cosmos in the near infrared.

"Keck's achievement in bringing this new technology to fruition marks
nothing less than a renaissance in ground based infrared astronomy,
equivalent to the day Galileo first turned his telescope to look at the
night sky," said Dr. Matt Mountain, director of the Gemini Observatory,
which operates twin 8-meter telescopes. "A profound impact of these
results is that it can enable a whole new class of extremely large 30
meter to 100 meter telescopes to obtain diffraction-limited images from
the ground."

Studying the center of our home galaxy, the Milky Way, is another of the
key scientific drivers for developing adaptive optics systems and
improving their performance. "The center of our galaxy is a very
difficult region to study from Hawaii because it rises only about 44
degrees above the horizon," said Dr. Antonin Bouchez, adaptive optics
researcher at the W. M. Keck Observatory. "The Galactic Center is also a
region in the sky heavily obscured by interstellar dust, and only a few
dim stars are available in that area for us to use as reference stars to
guide the adaptive optics system."

Despite these observing difficulties, which limited the ability to
correct the image blur, astronomers were previously able to use a guide
star 30 arcseconds away from the Galactic Center to study the motion of
individual stars in the very central region. This work helped confirm
the presence of a massive black hole at the center of our galaxy.

"With the laser guide star, we can place a far brighter reference star
right on top of the black hole and suddenly we've removed that 30
arcsecond penalty," added Dr. Bouchez.

The new guide star images show many more point sources in the central
region of the Galactic Center, and these stars are much better resolved
(Figure 1). Now, the black hole at the center of our galaxy is easy to
distinguish from other sources, even allowing scientists to witness a
giant flare as plasma material fell into the black hole. (Figure 2). The
new system can also be used to generate large, panoramic views of the
sky because it creates its own reference star in any given field. For
the Galactic Center, AO-corrected images over a large field of view (80
arcseconds) were assembled to study stars within five light years of the
central black hole region (Figure 3).

"Past studies have shown that several of the stars orbiting the black
hole seem surprisingly young, yet this is a paradox because stars cannot
be born in such a violent, turbulent region," said Andrea Ghez, head of
the Galactic Center group and professor of physics and astronomy at the
University of California, Los Angeles. "This wide-field image lets us
study how the young and old stars are distributed in relation to their
position to the black hole. With the laser guide star, we can do this on
a much larger scale than before."

The new images of the Galactic Center were obtained July 26, 2004 under
average turbulence conditions for Mauna Kea (0.4 arcseconds). Team
members responsible for the observations are Peter Wizinowich, team
lead, and Antonin Bouchez, Randy Campbell, Jason Chin, Scott Hartman,
Erik Johansson, Robert Lafon, David Le Mignant, Paul Stomski, Doug
Summers and Marcos van Dam, all from W. M. Keck Observatory.

Shared risk observations by a small number of astronomers will continue
on the LGS/AO system through July 2005. General observing with the
LGS/AO system will begin August 2005.

The laser guide star adaptive optics system was funded by the W. M. Keck
Foundation. The artificial laser guide star system was developed and
integrated in a partnership between the Lawrence Livermore National Labs
(LLNL) and the W. M. Keck Observatory. The laser was integrated at Keck
with the help of Dee Pennington, Curtis Brown and Pam Danforth.

The NIRC2 near-infrared camera was developed by CalTech, UCLA and the W.
M. Keck observatory (P.I. Keith Matthew from CalTech). The W. M. Keck
Observatory is managed by the California Association for Research in
Astronomy (CARA), a non-profit 501 (c) 3 corporation whose board of
directors includes members from the California Institute of Technology,
the University of California and the National Aeronautics and Space
Administration (NASA). For more information and accompanying figures,
please visit www.keckobservatory.org.


Media Contact:
Laura K. Kraft
W.M. Keck Observatory
65-1120 Mamalahoa Hwy.
Kamuela, HI 96743
(808) 885-7887

Go, Keck!

Now... anybody have some numbers on what kind of effective "seeing"
they're winding up with? There were some references in the image
captions to "resolution" in the milliarcseconds, but I don't know
if that's quite the same thing.

On the (comparably) small telescope I sometimes operate across the summit
from Keck, "seeing" ranges between roughly 0.3 and 1.3 (yeah, I know)
arcseconds. I've heard that with AO and the laser guide stars, the
decimal would be moving over a place or two... anyone know?

-Dan

--
Dan Birchall, Hilo HI - http://dan.birchalls.net/ - images, words, technology