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Getting the picture in the infrared.

Getting the picture in the infrared

In the film "Wolfen," special effectsgive the audience a view of the world through the eyes of a pack of superwolves, whose eyes presumably can sense and image infrared. Now astronomers have something similar, devices to put on telescopes that can make an image with infrared radiation analogous to what human eyes do with visible light. The first of these infrared array detectors are being applied to telescopes belonging to the National Optical Astronomy Observatories (NOAO).

Previously astronomers working inthe infrared had to build up pictures of the sky by "rastering," or measuring the infrared brightness of the sky, point by point, realigning the telescope for each point. The new detectors operate like human eyes, as well as like photographic plates and charge-coupled devices (CCDs) that visible-light astronomy uses, making an image of a portion of the sky all at once. Furthermore, according to NOAO, they do it with greater sensitivity and resolution than infrared has ever had before.

Like CCDs also, the new infraredimagers involve the latest photoelectric technology and were originally developed for military and intelligence uses. (As Albert Fowler, the NOAO engineering manager for this project, puts it, astronomy doesn't have the money it takes to fund state-of-the-art infrared. The Defense Department does.)

The new detectors replace the singleinfrared sensor used in rastering with an array of indium antimonide sensors about the size of a flake of confetti. The array is mounted on a silicon microchip that reads out the data and sends them to a computer system, called the Image Reconstruction and Analysis Facility, that draws the picture. These sensors are as much as 100 times as sensitive as the ones they replace.

So far, the new array detectors havebeen used with the 50-inch and 84-inch telescopes at the Kitt Peak National Observatory near Tucson, Ariz. "For many applications at these wavelengths [1 to 5 microns]," says Frederick Gillett, a Kitt Peak astronomer who is project scientist on the infrared-detector team, the 50-inch telescope has thus become "the most powerful infrared telescope in the world." However, he sounds eager to get the detectors on a 4-meter-class telescope. Such a coupling will produce "an altogether new game," he says. "You can carry out observations you wouldn't have dreamed of doing in the past."

Among the areas of astronomy inwhich infrared of this range is particularly useful are: searches for areas where new stars are forming; searches for dark companions, either planets or brown dwarf stars, bound to visible stars; surveys of redshifts and therefore distances of other galaxies; investigations of the center of our own galaxy, which is obscured in visible light but comes through in infrared; and studies of the planets of our own solar system. "The second night we had this array, we imaged the rings around Uranus," Gillett says.

The Santa Barbara Research Center, asubsidiary of Hughes Aircraft, developed the arrays. Of the four now in existence, one will soon go the Cerro Tololo Inter-American Observatory at La Serena, Chile. Eventually the 50-inch, 84-inch and 4-meter telescopes at Kitt Peak and the 50-inch and 4-meter telescopes at Cerro Tololo will get them.
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Title Annotation:devices for telescopes that make an image with infrared detection
Author:Thomsen, Dietrick E.
Publication:Science News
Date:May 9, 1987
Words:524
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