Flight Day, May 7, 1994
by Jesse Bregman, Astronomer
KAO flight 5/7/94 from Honolulu to Honolulu
Last night's flight didn't last very long since a crucial piece of the telescope, called the chopping secondary, did not work. Observing in the infrared (light with wavelengths between about 1 and 1000 micrometers, and far redder than the reddest light we see with our eyes) is difficult since everything at room temperature glows brightly at these wavelengths. It is similar to trying to observe stars with you eyes during the day. To accomplish this difficult task, we use a mirror which rocks back and forth , alternately putting the object we want to observe and blank sky on our detectors. The mirror moves back and forth 7 times per second, and we have programmed our computers to read the light intensity in our spectrometer* at the same rate. This technique enables us to measure signals that are 10,000 to 100,000 times weaker than the general glow of our surroundings. The moving mirror is called a chopper, and it was this part of the telescope that was not working.
The KAO staff will most likely be able to fix the chopper so we can have a good flight on Monday to do the observations planned for last night. If the chopper had worked, we would have observed a few more bright infrared stars in icy regions, similar to t hose on the first flight on May 5. We also had a group of objects on the list which are completely different. Instead of showing the chemical nature of the material surrounding the star by absorbing light from the star, we can tell what is around the stars by the light that the gas emits, having been excited by ultraviolet (bluer than our eyes can see) light from the stars. We have evidence that this material is similar to the soot that comes out of car exhaust and leaves the black marks you see on the road. They are called polycyclic arom atic hydrocarbons (PAHs) and are very large molecules, especially by astronomical standards, composed entirely of carbon and hydrogen. The observations we had planned would test this idea by searching for emission features which others at NASA Ames have f ound in laboratory spectra of PAHs. Finding these new features in the spectra of the objects we will look at with the KAO telescope will confirm that these molecules are indeed PAHs. We will then be able to use spectra of PAH molecules to determine the ki nds of environments in which the molecules can exist. It may be that when the earth was formed, PAHs were included and became the building blocks for more complex organic molecules which eventually led to life on our planet.
* (Note by Edna DeVore) The spectroscope is the instrument attached to the KAO telescope which allows astronomers to spread out the infrared radiation like a prism or diffraction grating spreads out visible light into a band of colors cal led the spectrum. When the infrared radiation is spread out, astronomers can look at a small piece of the spectrum, and see bright (emission) or dark (absorption) lines. These strength of the lines (the "signal strength") is stored as numbers in a compute r for later analysis and comparison with the spectra of dust and ice viewed by spectroscopes in the laboratories at NASA Ames. By comparing the spectra of astronomical objects with the spectra of dust and gas that is of known composition, the astronomers are able to identify the composition of the dust and gas in space.
Jesse Bregman, Astronomer