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2\04 Astronomers Get Ultrasharp Images With Large Telescope In Arizona
Part 1 of 2

ASTRONOMERS GET ULTRASHARP IMAGES WITH LARGE TELESCOPE IN ARIZONA
From Lori Stiles, UA News Services, 520-621-1877
February 4, 2003

Astronomers have successfully tested a new method to remove 
atmospheric blurring from large ground based telescopes.

The experiments were made in November 2002 and January 2003 at the 
6.5-meter (21-foot) telescope at the MMT Observatory on Mount Hopkins, 
Ariz. The project is a collaboration of the University of Arizona's 
Steward Observatory and Italy's Osservatorio Astrofisico di Arcetri in 
Florence. It uses revolutionary new technology developed with support 
from the U.S. Air Force.

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FOR PHOTOS, IMAGES AND MOVIES OF THIS EXCITING NEW PIECE OF IMAGING
TECHNOLOGY IN ACTION, SEE http://athene.as.arizona.edu/~lclose/AOPRESS
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Large ground based telescopes can make images as sharp as or sharper 
than the Hubble Space Telescope, but only if atmospheric blurring is 
corrected.  Previously, the deformable mirrors available to do this 
were small, flat, and relatively inflexible. They could be used only 
as part of complex instruments attached to conventional telescopes.

But in this new work, one of the two mirrors that make up the 
telescope optics is used to make the correction directly. The new 
secondary mirror makes the entire correction with no other optics 
required, making for a more efficient and cleaner system.

Like other secondary mirrors, this one is made of glass over 2 feet in
diameter and is a steeply curved dome shape. But under the surface, it 
is like no other. The glass is less than 2 millimeters thick (less 
than eight-hundredths of an inch). It literally floats in a magnetic 
field and changes shape in milliseconds, virtually real-time. 
Electro-magnetically gripped by 336 computer-controlled "actuators" 
that tweak it into place, nanometer by nanometer, the adaptive 
secondary mirror focuses star light as steadily as if Earth had no 
atmosphere. Astronomers can study precisely sharpened objects rather 
than blurry blobs of twinkling light.

"The reason no one has done this before is because it turns out to be
enormously technically challenging," said Michael Lloyd-Hart of the UA
Center for Astronomical Adaptive Optics (CAAO), project scientist for 
the MMT adaptive optics system. Lloyd-Hart and chief system engineer 
Francois Wildi led the design and engineering effort. "We found out 
the hard way just how difficult it is. It's taken us a number of years 
to build a mirror with a shape that deforms in real time," Lloyd-Hart 
said.

One of the system's unique features is its ability to make corrections
according to the detail of the distortion measurements. If very faint 
stars provide no useful data, the shape can be fixed to mimic a 
conventional mirror of solid glass. The mirror can also be used to 
rapidly "chop" the viewpoint of the telescope, as required for 
infrared imaging.

"It's been 25 years or so since anyone's tried a radically new way of
building a deformable mirror, and this technology really is different, 
"said Laird Close, UA assistant professor of astronomy and CAAO 
scientist.  "But the ability to build large, curved, deformable 
mirrors for adaptive optics is a boon to astronomers using the giant 
new ground-based telescopes."

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Contact Information
Michael Lloyd-Hart
520-621-8353  mhart{at}as.arizona.edu

Laird Close
520-626-5992  lclose{at}as.arizona.edu

Philip M. Hinz
520-621-7866 phinz{at}as.arizona.edu

Francois Wildi
520-626-6720 fwildi{at}as.arizona.edu

Guido Brusa
520-626-9529 gbrusa{at}as.arizona.edu
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"The adaptive secondary mirror made for the UA and Smithsonian 
Institution's 6.5-meter telescope at the MMT Observatory is a 
tremendous advance over conventional adaptive optics, which are 
systems that involve extra relay optics and mirrors in a box separate 
from the telescope, Lloyd-Hart said.

"One key feature is that we correct for blurring effects of the 
atmosphere at a mirror which is an integral part of the telescope," 
Lloyd-Hart said.  "The conventional approach has been to build the 
telescope, then build a box of optical tricks to improve the resolving 
power of the telescope."

The new system solves a big problem astronomers face when they try to
observe at longer infrared wavelengths, where special targets like
Jupiter-like planets and circumstellar disks are brightest.

"Everything in the world glows with thermal energy, or heat. When you 
try to do astronomy at those wavelengths, even the optics that you are 
looking through glow. So the more optical surfaces and telescope parts 
you can eliminate ­ the simpler the system is optically, the better it 
is for doing infrared astronomy," Lloyd-Hart said.

The Steward Observatory Mirror Lab made the MMT's large deformable 
convex, aspheric secondary mirror. Learning how to make glass 2mm 
thick so that it's "infinitely floppy" was a major challenge to 
building the system, Lloyd-Hart said.

The biggest equivalent flexible mirror available commercially at this 
time is 12 cm, or about 4 and 3/4 inches, across, Close said.

But once Steward Observatory researchers realized how to do it, they 
also realized they could make big deformable mirrors for use in space. 
Steward Observatory has been developing new space-based optics as a 
spin-off of this ground-based technology.

The Italian partners designed very powerful computer electronics that 
drive the MMT's adaptive secondary mirror with a cluster of 168 
microprocessors, which are all packed in an electronics crate that is 
mounted behind the secondary mirror. The computer cluster is 
essentially a supercomputer, more powerful than any computer available 
during the Apollo space era. It senses the positions of and drives the 
actuators.

Guido Brusa, CAAO/Large Binocular Telescope adaptive optics scientist, 
said that he is "personally very happy" with the results of effort, 
achieved during the past 7 to 8 years through "patient and persevering 
work of many people in both Arizona and Italy....It is great to see 
that the adaptive secondary mirror performs beautifully, even in the 
presence of relatively strong wind (20 to 30 mph) and in environmental 
conditions very different from those in the lab."

Brusa called the success "an important step" in integrating adaptive 
optics into an astronomical telescope. An adaptive primary telescope 
mirror is "a foreseeable future development," he said.

(continued)

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