By ANDY FLEMING
This image, obtained during the late commissioning phase of
the GeMS adaptive optics system, with the Gemini South AO Imager (GSAOI) on the
night of December 28, 2012, reveals exquisite details in the outskirts of the Orion
Nebula. The large adaptive optics field-of-view (85 arcseconds across)
demonstrates the system's extreme resolution and uniform correction across the
entire field. The three filters used for this composite color image include [Fe
II], H2, and, K(short)-continuum (2.093 microns) for blue, orange, and white
layers respectively. The natural seeing while these data were taken ranged from
about 0.8 to 1.1 arcseconds, with AO corrected images ranging from 0.084 to
0.103 arcsecond. Each filter had a total integration (exposure) of 600 seconds.
In this image, the blue spots are clouds of gaseous iron "bullets"
being propelled at supersonic speeds from a region of massive star formation
outside, and below, this image's field-of-view. As these "bullets"
pass through neutral hydrogen gas it heats up the hydrogen and produces the
pillars that trace the passage of the iron clouds. (Image Credit: Gemini
Observatory/AURA)
A new image released today reveals how Gemini
Observatory's most advanced adaptive optics (AO) system will help astronomers
study the universe with an unprecedented level of clarity and detail by
removing distortions due to the Earth’s atmosphere. The photo, featuring an
area on the outskirts of the famous Orion Nebula, illustrates the instrument's
significant advancements over previous-generation AO systems.
"The combination of a constellation of five
laser guide stars with multiple deformable mirrors allows us to expand
significantly on what has previously been possible using adaptive optics in
astronomy," said Benoit Neichel, who currently leads this adaptive optics
program for Gemini. "For years our team has focused on developing this
system, and to see this magnificent image, just hinting at its scientific
potential, made our nights on the mountain - while most folks were celebrating
the New Year’s holiday - the best celebration ever!"
The new system, called GeMS, is installed on the
Gemini South telescope in Chile and is the first of its kind to use laser guide
stars and a technology called Multi-Conjugate Adaptive Optics (MCAO) to image
the sky. Motivated by MCAO's potential to produce a significantly larger
field-of-view and more uniform corrections than previous AO systems, former
Gemini scientist François Rigaut (now at the Australian National University),
first suggested the system's development at Gemini over 10 years ago. According
to Rigaut, "It's a great feeling to see this system on the sky and doing
cutting-edge science. When it's all theoretical you dream of what it will
someday do to improve our vision of the cosmos. An image like this makes it so
real - it's worth all the mental sweat!"
"Adaptive optics allows ground-based
telescopes to take full advantage of their large mirrors,” notes Dr. Gary
Schmidt, Gemini program director for the U.S. National Science Foundation.
“Gemini's development of MCAO leads the world, and its fidelity even surpasses
that of current – and far more expensive – orbiting observatories for imaging
the sky."
This milestone also bodes well for future
generations of large ground-based telescopes. "As telescopes get larger
they look through more and more of the Earth's atmosphere and this is a
problem,” said Gary Sanders, Project Manager of the 30-Meter Telescope (TMT)
Project. Sanders emphasizes that it is imperative that we find new and
innovative ways to solve this problem by removing the distortions caused by the
turbulent air overhead. “MCAO is a key technology that makes the next
generation of large telescopes, like the TMT, justifiable. It allows us to use
the light we collect more efficiently and see the universe more sharply than
ever before in human history," said Sanders.
About five years ago, when GeMS was under
development, and still just a vision for Rigaut and the team, Gemini
Observatory released an image of a smaller section of this area of the Orion
Nebula known as the "Orion Bullets." That image demonstrated the
power of Gemini's AO system called Altair - which is still actively used at the
Gemini North telescope. Gemini’s instrument scientist for Altair, Chad
Trujillo, points out that in one shot GeMS covers a significantly larger
field-of-view than Altair and, he adds, “The uniformity and performance across
the image is amazing! In this new image, the pixels are 2.5 times finer and
there are about 16 times more of them. Both the correction quality and the
field-of-view are considerably better than the previous generation of AO
systems.”
THE MCAO ADVANTAGE
The technology behind MCAO involves the use of
multiple laser guide stars (five in the GeMS system) and several deformable
mirrors (three in all) to sample atmospheric distortions and cancel them out in
real-time as imaging data is collected. Using algorithms similar to those
developed for medical tomographic imaging the GeMS MCAO system creates a
three-dimensional snapshot of atmospheric turbulence about 500 to 1000 times
per second. The result is about a 16-fold increase in the patch of sky
observed, while providing uniform corrections over the entire field. "This
is huge when it's time for astronomers to reduce their data," said Adam
Ginsburg a graduate student working with John Bally at the University of
Colorado who originally proposed that the GeMS system revisit the Orion bullets.
"If the corrections are not uniform across the entire field it is
difficult, and sometimes impossible, for researchers to compare one part of a
dataset with another and errors proliferate,” said Ginsburg. Bally adds that
MCAO should make this problem a non-issue.
GeMS, in conjunction with the Gemini South
Adaptive Optics Imager (GSAOI), is undergoing commissioning and has obtained
some early System Verification data. About 80 hours have been offered for the
first semester of 2013, and more will be available in the second semester, for
astronomers in the international partnership through the standard Gemini
proposal process.
THE ORION BULLETS
Discovered in 1983, the Orion Bullets are clumps
of gas ejected from deep within the Orion Nebula - located some 1500 light-years
from our Solar System. The violence causing this is likely related to the
recent formation of a cluster of massive stars with strong winds that can expel
gas at supersonic speeds. The bullets (seen as distinctive blue features in the
new Gemini image) are actually quite large, about 10 times the size of Pluto’s
orbit around the Sun.
As the bullets speed outward, they leave behind
distinctive tubular and cone-shaped wakes, which shine like tracers due to the
bullets heating of the molecular hydrogen gas in the Orion Nebula. The wakes
span much greater distances than the bullets, measuring as much as a fifth of a
light-year in length. As Gemini first observed with Altair, the fingerlike
wakes also resolve into filaments which are clearly resolved in the new Gemini
GeMS image.
Original Source: Gemini Observatory
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