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Posted by baalke on September 5, 2007, 9:12 pm
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http://mr.caltech.edu/media/Press_Releases/PR13030.html
Caltech Astronomers Obtain Sharpest-Ever Pictures of the Heavens
Caltech News Release
September 4, 2007
PASADENA, Calif. - Astronomers from the California Institute of
Technology and the University of Cambridge have developed a new camera
that produces much more detailed pictures of stars and nebulae than
even
the Hubble Space Telescope, and it does all this from here on Earth.
Until now, images from ground-based telescopes have been invariably
blurred by Earth's atmosphere. Astronomers have developed a technique,
known as adaptive optics (AO), to correct the blurring, but so far it
has only worked successfully in the infrared, where the smearing is
greatly reduced. However, a new noise-free, high-speed camera has been
developed at the Institute of Astronomy in Cambridge that, when used
behind the infrared Palomar Adaptive Optics System, at last makes very
high resolution imaging possible in ordinary visible light.
The camera works by recording partially corrected adaptive optics
images
at high speed (20 frames per second or more). Software then checks
each
image to sort out which are the sharpest. Many are still significantly
smeared by the atmosphere, but a small percentage of them are
unaffected. These are combined to produce the final high-resolution
image that astronomers want. The technique is called "Lucky Imaging"
because it depends on the chance fluctuations in the atmosphere
sorting
themselves out and providing a set of images that is easier for the
adaptive optics system to correct.
This work was carried out on the 200-inch (5.1 meter) Hale Telescope
on
Palomar Mountain. Like all other ground-based telescopes, the images
it
normally produces are typically 10 times less detailed than those of
the
Hubble Space Telescope. Palomar's adaptive-optics system produces
superb
images in the infrared, but until now, its images in visible light
have
remained markedly poorer than Hubble images. With the new Lucky
Camera,
astronomers were able to obtain images that are twice as sharp as
those
produced by the Hubble Space Telescope-a remarkable achievement.
The images produced in the study are the sharpest direct images ever
taken in visible light either from the ground or from space. "The
system
performed even better than we were expecting. It was fantastic to
watch
the first images come in and see that we were easily doing better than
Hubble," says Nicholas Law, a postdoctoral scholar at Caltech and
principal investigator for the instrument.
Most astronomical objects are so far away that astronomers are
desperate
to see more and more detail within them. The new pictures of the
globular star cluster M13, located 25,000 light years away, are sharp
enough that astronomers are able to find stars as little as one
light-day apart. A light-year is the distance light travels in one
year
(almost 6 trillion miles). A light-day is the distance light travels
in
just one day. Stars in the vicinity of the solar system are much
farther
apart -the nearest star to our solar system is over four light-years
away.
The astronomers also observed very fine detail in objects such as the
Cat's Eye Nebula (NGC 6543). It is eight times closer to earth than
M13,
allowing filaments that are only a few light-hours across to be
resolved.
The use of the camera at Palomar was a demonstration of the potential
of
visible-light adaptive optics and offers a glimpse of the detailed
imagery to come. Astronomers at Caltech and the Jet Propulsion
Laboratory are currently developing the first-ever astronomical
adaptive-optics system fully capable of capturing visible-light
images.
The new system, known as PALM-3000, will routinely allow the 200-inch
telescope at Palomar to outperform the Hubble Space Telescope at even
blue wavelengths. Using state-of-the-art deformable mirrors, sensors,
and a powerful laser, the upgraded Palomar adaptive-optics system will
provide finer correction of the atmospheric blurring than any present
adaptive optics system, allowing long-exposure images with the same
fine
detail as the "lucky" images taken recently.
Caltech's Richard Dekany, principal investigator for PALM-3000, says
that the upgraded instrument could be available as early as 2010.
"These
Lucky Imaging results underscore the science potential of
diffraction-limited visible-light observations on large ground-based
telescopes," he explains.
To get even sharper pictures, astronomers will need to use bigger
telescopes. The results open up the possibility of further
improvements
on even larger telescopes, such as the 10-meter Keck telescopes on the
top of Mauna Kea in Hawaii or in the future even larger telescopes,
such
as the Thirty Meter Telescope (TMT).
Working on the Lucky Imaging project were Law, Dekany, Mike Ireland,
and
Anna Moore from Caltech and the Palomar 200-inch crew. Other team
members included Craig Mackay from Cambridge, James Lloyd from Cornell
University, and Peter Tuthill, Henry Woodruff, and Gordon Robertson
from
the University of Sydney.
Images are available at
http://www.astro.caltech.edu/~nlaw/lucky_palomar/ and
http://www.astro.caltech.edu/palomar/AO/luckycam.html.
Contacts:
Nicholas Law, postdoctoral scholar California Institute of Technology
(626)-395-2223 (US)
Craig Mackay, reader in image science Institute of Astronomy,
University
of Cambridge phone: +44 (0)1223 337543 (UK)
Scott Kardel, public affairs director Palomar Observatory e-mail:
742-2111
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