Poor Hubble Space Telescope. While work on the orbital observatory's replacement moves ahead, along comes new images from Hawaii's Gemini Observatory to add insult to injury.
Armed with a new imaging spectrograph, the Gemini Observatory recently captured images that are among the sharpest ever obtained of astronomical objects from the Earth, all without the help of adaptive optics.
One of the limitations of ground-based astronomy is the Earth's atmosphere, which distorts light traveling through it. When viewing large objects or regions of the sky, the distortion is not tremendously troublesome, but as astronomers try to view smaller and smaller areas of the heavens, the distortion becomes more and more noticeable.
Adaptive optics remedies this problem by using what is known as a deformable mirror. This mirror is manipulated as many as a thousand times a second to compensate for any blurriness the air causes.
However, the Gemini Multi-Object Spectrograph (GMOS) on the 8-meter Gemini South Telescope in Cerro Pachón, Chile, takes the concept of adaptive optics to a higher level, as a new image of the Hickson Compact Group 87 (HCG87) clearly illustrate. (See accompanying images at right.) Previously only seen from space, HCG87 is a diverse group of galaxies located about 400 million light years away in the direction of the constellation Capricornus. HCG87 was imaged with the Hubble Space Telescope in 1987.
"Historically, the main advantage of large ground-based telescopes, like Gemini, is their ability to collect significantly more light for spectroscopy than is possible with a telescope in space," said Phil Puxley, Associate Director of the Gemini South Telescope said in a release. The Chilean instrument, and its twin the Gemini North Telescope at Mauna Kea, Hawaii make up the Gemini Observatory controlled from Hilo, Hawaii. "The Hubble Space Telescope is able to do things that are impossible from the ground. However, ground-based telescopes like Gemini, when conditions are right, approach the quality of optical images now only possible from space. One key area -- spectroscopy of faint objects, which requires large apertures and fine image quality -- is where large telescopes like Gemini provide a powerful, complementary capability to space-based telescopes."
GMOS-South is currently undergoing commissioning on the 8-meter Gemini South Telescope in Chile. "GMOS-South worked right out of the box, or rather, right out of the 24 crates that brought the 2-ton instrument to Chile from Canada and the UK - just like its northern counterpart did when it arrived on Hawaii's Mauna Kea," says Dr. Bryan Miller, head of the commissioning team.
"The GMOS program demonstrates the advantage of building two nearly identical instruments. Experience and software from GMOS-North have helped us commission this instrument more rapidly and smoothly than we could have done otherwise," explains Dr. Miller. "Although the images from GMOS-South are spectacular, the instrument is primarily a spectrograph and that is where its capabilities are most significant for scientists." GMOS-South is expected to begin taking science data in August 2003.
As a multi-object spectrograph, GMOS is capable of obtaining hundreds of spectra, or data sets describing the various wavelengths of light an object emits, in one "snapshot." The ability to deliver high-resolution images is a secondary function.
"It used to take an entire night to obtain one spectrum," explains Dr. Inger Jørgensen, who led the commissioning of the first GMOS instrument on the Frederick C. Gillett Gemini Telescope (Gemini North) over a year ago. "With GMOS, we can collect 50-100 spectra simultaneously. Combined with Gemini's 8-meter mirror, we are now able to efficiently study galaxies and galaxy clusters at vast distances - distances so large that the light has traveled for half the age of the Universe or more before reaching Earth. This capability presents unprecedented possibilities for investigating how galaxies formed and evolved in the early Universe."
GMOS achieves this remarkable sensitivity partly because of its technologically advanced detector, which consists of over 28 million pixels, and partly because of multiple innovative features of the Gemini dome and telescope that reduce local atmospheric distortions around the telescope. "When we designed Gemini, we paid careful attention to controlling heat sources and providing excellent ventilation," said Larry Stepp, former Gemini Optics Manager. Stepp elaborates, "For example, we constructed 3-story-high vents on the sides of the Gemini enclosures. It is great to see this image that provides such a dramatic validation of our approach."
"The twin Gemini Telescopes offer a unique advantage," explains Director of the Gemini Observatory Dr. Matt Mountain. "Now that both telescopes are equipped with nearly identical GMOS instruments, we have created an unprecedented uniform platform to coherently study and take deep spectra of any object in the northern or southern sky at optical wavelengths."
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