This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2\04 Astronomers Get Ultrasharp Images With Large Telescope In Arizona
Part 2 of 2

In the MMT's new adaptive optics, a wavefront sensor camera mounted at 
the base of the telescope senses atmospheric turbulence and sends that
information to the MMT adaptive secondary mirror. The powerful 
computer cluster behind the secondary mirror sends electronic current 
through coils so that each of 336 actuator magnets spaced across the 
mirror is instantly moved to the desired position. The result is a 
"flat," non-wavy wavefront seen by the astronomer's science camera.

The unique adaptive optics system also includes its own plumbing. Its
half-water, half-methanol liquid cooling system can dissipate up to a
kilowatt of heat.

DETWINKLING AND BLOCKING STARLIGHT

UA astronomer Phil Hinz' observing run Jan. 22 illustrates why the new
adaptive optics system is ideal if you're looking for planetary disks 
or planets around bright, nearby stars.

On Jan. 22, Hinz and UA astronomer emeritus Bill Hoffmann took Hinz' 
nulling interferometer called "BLINC" and Hoffman's infrared
"MIRAC" 
camera to the MMT, while UA, Italian and Smithsonian Institution MMTO 
staff ran the new adaptive optics.

"Without adaptive optics, nulling interferometry is able to suppress 
the star to only 5 to 10 percent of its original brightness," Hinz 
said. "In addition, the intensity of the star rapidly changes because 
of atmospheric turbulence, so the star appears to blink on and off."

Nulling interferometry works by creating two "sub-telescopes," both 
looking at the same bright star, but positioned so starlight from each 
sub-telescope travels in slightly different paths before hitting the 
detector. When properly aligned, crests of lightwaves from one 
sub-telescope will line up with the troughs of the lightwaves from the 
other, in effect canceling the light of the bright star.

Hinz, who used the 6.5-meter MMT as two 3-meter sub-telescopes, said 
the initial Jan.22 observations were successful in showing the power 
of adaptive optics to stabilize the star and suppress all but two 
percent of its light.

"Once we've refined this technique, we should be able to stabilize and
suppress all but one-tenth of a percent, down to three-hundredths of a
percent of the starlight and see faint, planetary dust disks much like 
our own solar system around nearby stars," Hinz said.

"Our own dust disk is about one-hundredth of one percent of the 
brightness of the sun, which sets the ultimate goal of this technique. 
This is the level of suppression we're aiming for with the Large 
Binocular Telescope Interferometer," he added.

ADAPTIVE OPTICS FOR THE LBT

University of Arizona scientists are developing two adaptive secondary
mirrors for the Large Binocular Telescope (LBT) on Mount Graham, said 
UA astronomer John Hill, who directs the LBT project. The LBT won't 
have conventional secondary mirrors, Hill said. Each of the LBT's 
8.4-primary mirrors will have an adaptive concave (rather than convex) 
secondary mirror 91 cm (36 inches) across, held by 672 actuators that 
will bend it moment by moment to the required shape.

In principle, even a 6.5-meter ground-based telescope could be used to 
image a Jupiter-like planet in a solar system like our own within the 
8 parsec neighborhood, Mirror Lab director and CAAO director Roger 
Angel has noted in research papers. (Eight parsecs is about 26 
light-years, or more than 153 trillion miles.)

As for the really giant telescopes of the future ­ telescopes with
20-meter-or-more diameter primary mirrors ­ ground based telescopes 
with adaptive secondary mirrors should be able to directly detect and 
study nearby Earth-like planets, Angel predicts.

Success in making deformable adaptive secondary mirrors for large 
telescopes is "a natural stepping stone to so-called 
'multiple-conjugate adaptive optics,'" Lloyd-Hart said. This system 
would use several deformable mirrors in series and correct for 
atmospheric turbulence in 3 dimensions.

"You could cancel the atmospheric error anywhere you look. You'd have 
a very large field of view with high resolution all at once. And when 
you can capture huge fields of view and see them with extreme clarity, 
then you're talking real scientific progress," Lloyd-Hart said.

 - End of File -
================

---