ground-based telescopes

Heat is the enemy in the National Optical Astronomy Observatories` nine telescope domes on Kitt Peak, about 50 miles outside of Tucson, AZ. As unwanted thermal energy rises to escape though a dome`s slit, it passes in front of the telescope mirror and distorts the light reaching the telescope, causing blurring and loss of detail. This makes it more difficult to identify and measure individual stars, in particular within galaxies. To hel¥locate the sources of the undesirable heat, scientists

ground-based telescopes

Astronomers monitor observatory with IR cameras

Heather W. Messenger

Heat is the enemy in the National Optical Astronomy Observatories` nine telescope domes on Kitt Peak, about 50 miles outside of Tucson, AZ. As unwanted thermal energy rises to escape though a dome`s slit, it passes in front of the telescope mirror and distorts the light reaching the telescope, causing blurring and loss of detail. This makes it more difficult to identify and measure individual stars, in particular within galaxies. To hel¥locate the sources of the undesirable heat, scientists at the observatories purchased a Thermovision 488 infrared imaging system from AGEMA Infrared Systems (Secaucus, NJ).

"In the 1960s, when the domes on Kitt Peak were built, not a lot of attention was paid to this problem," says George Jacoby, staff astronomer at the facility, which is funded by the federal government through AURA Inc., a consortium of US universities. "As a result, we estimate there`s about 10 kW of unnecessary thermal energy in some of our domes. If we can reduce that level to 1 kW or less, we can increase the quality of our telescopic images by more than a factor of two! This is equivalent to replacing the mirrors in our telescopes with ones 60% larger in diameter, a project that would cost nearly $10 million."

The real-time infrared imager, which can detect temperature differences smaller than 0.1°C, provides color images and measurement data. Using the infrared imaging camera in the observatories` largest two domes, to date Jacoby has already identified sources that account for at least one half of the 10 kW of heat. "As they rotate, the telescopes ride on bearings that are lubricated by oil under pressure," says Jacoby. The oil heats and contributes, by his estimate, about 4 kW.

The control rooms from which astronomers conduct their observations is another big contributor. The temperature inside the domes is nearly the same as the outside air (30°F-40°F) but the control rooms are heated to between 65°F and 70°F. The camera was able to find major leaks around the doors and large windows through which observations are made. Just fixing those leaks and turning unnecessary lights off during the day will probably reduce the observatory`s electric bill enough to pay for the camera.

Another source of heat detected by Jacoby and his fellow staff astronomers Taft Armandroff and Michael Pierce is the electronic equipment that collects and records the data. Other than adding insulation to the control room walls where possible, the resolution for these heat sources will likely happen as equipment is replaced or updated. The selection of new instruments will be driven by the amount of heat they generate.

Jacoby also plans to use the camera at a tower in Tucson where they evaluate new telescope mirrors. Jacoby adds, "We`ve done some preliminary scanning in there and found that it contains a badly insulated heating duct that`s throwing off enough heat to be a factor in our mirror evaluations." He guesses that he will kee¥finding reasons to check for unwanted heat, saying, "As modifications are made to the domes and new equipment is installed or facilities constructed, there will always be a need for the thermal imaging camera."

More in Optics