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by Nathan Whalen
After delays resulting from mechanical problems with the Hubble Space Telescope, researchers continued their examination of dwarf galaxies in an effort to expand their understanding of the formation of stars.
Evan Skillman, an astronomy professor at the University of Minnesota, was recently granted access to the Hubble Telescope. In an effort to fill gaps in previous research, Skillman is using the telescope to gather more information on the Sextans A dwarf galaxy. The delay in research occurred when an infrared camera on the Hubble Telescope was found to be defective. Usually, the infrared camera lasts three years. But a coolant leak would render the camera useless in about a year, so researchers who needed the camera were therefore given priority to use the telescope. Because Skillman’s research does not depend on the use of the camera, he couldn’t get access to the telescope until last April.
In June 1997, Skillman used the Hubble Telescope to observe the Sextans A, Leo A, Pegasus DIG, and the GR8 dwarf galaxies. The results, which were presented in a paper in September, 1998, showed that the Sextans A galaxy went through a period of intense star formation about 300 million years ago and these "younger" stars could be easily distinguished from older, helium-burning stars, which can be up to tens of billions of years old.
"We didn’t expect to see those two populations distinguish themselves like that," Skillman said.
Data collected from the GR8 dwarf galaxy suggested that star formation occurred in one region of the galaxy, moved to a different region, and then moved back to a region that has had previous star formation.
"It looks like gas clouds are more robust and not easily destroyed," Skillman said. Data collected from the Pegasus DIG and Leo A galaxies showed lower occurrences of star formation. According to Skillman, because of the low occurrences of recent star formation, a pattern of movement in these galaxies could not be seen.
Last April, when Skillman was again given access to the Hubble Telescope, he collected more data on the Sextans A dwarf galaxy. The goal of these new observations and the ones to be conducted in August is to get images of the faintest stars possible. "This is like opening up the shutter on a camera for a longer period of time," explains Skillman. That is, the longer the shutter is open on a camera, the more information will be on a photo.
This is the same concept with the Hubble Telescope; the more time the telescope spends observing a star, the more detailed the images will be. For example, in August, the Hubble Telescope will look at the Sextans A galaxy while making twenty-five orbits around Earth.
The goal for researchers is to extract more information from faint stars. One problem with photographing faint stars is that the image blurs so much that between twenty-five and fifty percent of the stars will not appear in the photograph. As a result, researchers cannot get an accurate census of stars. According to Skillman, the number of older stars in a galaxy helps determine the age of that galaxy.
When Skillman gets access to the Hubble Telescope in August, he will also get a series of observations of ISTC 1613, a local dwarf galaxy which is closer and larger than Sextans A. Skillman hopes that he will be able to determine the age of ISTC 1613. Skillman coordinates this project with researchers at the University of Wisconsin, Madison, the University of Michigan, Ann Arbor, the National Optical Astronomy Observatory in Tucson, Arizona, and the European Southern Observatory in Munich, Germany. This is a period of transition for Skillman as he and his research team are bombarded with tremendous amounts of information after delays that were out of his control. He wants to have results for this latest research before the information that Hubble Telescope provides become part of the public domain and thus can be accessed by other researchers one year after the observations take place.
