ASTRONOMERS RESOLVE A DOUBLE STAR SYSTEM IN AQUARIUS AND OBSERVE PECULIAR MOTION OF ITS JET AT RADIO WAVELENGTHS

PRESS RELEASE NO.: 97-78

Astronomers announced today they have for the first time seen the individual stars which form an enigmatic double star system in the constellation Aquarius and discovered that jets of material being ejected from of one of the stars have a peculiar sideways motion. The result is of special interest because it offers new insight into the behavior of a class of objects known as symbiotic stars.

The report is being presented today by Dr. Jeffrey A. Pedelty of NASA's Goddard Space Flight Center in Greenbelt, Md. to the American Astronomical Society summer meeting in Winston-Salem, N.C. Others involved in the research team are Dr. Mike Hollis and Mr. Rick Lyon (both also from Goddard), and Dr. Menas Kafatos of the George Mason University in Fairfax, Va.

The research team used the world's most powerful radio telescope to see new detail in the symbiotic star system called R Aquarii, a binary system in which a large red giant star and a much smaller and hotter companion star orbit one another.

"Being able to separate the two stars is like seeing the two headlights on a compact car in Los Angeles using a telescope in Washington, D.C," says Pedelty, a scientist with the Laboratory for Terrestrial Physics at Goddard. This is roughly twice the detail that can be seen with the Hubble Space Telescope.

Prior to these observations the two stars could not be separated by even the keen eyes of the Hubble Space Telescope. The astronomers used an array of 27 radio telescopes in New Mexico known as the Very Large Array (or VLA), operated by the National Radio Astronomy Observatory. The telescopes are connected to operate as if they were a single telescope with a diameter of 20 miles.

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The observations were made using a radio light wavelength of seven millimeters (the shortest wavelength achievable with the VLA). The combination of the short wavelength and large telescope size resulted in very fine detail.

The astronomers found that the two stars on the average are separated by "only" one and a half billion miles, roughly three times the average distance between the Earth and Jupiter. However, the two stars appear to be so close to each other because they are at a distance of about 600 light years (about 4,000 trillion miles) from the Earth.

On close approach, the two stars can strongly affect each other. For example, the strong gravity of the compact companion pulls material from the red giant, which spirals onto the compact star and forms a flat disk of hot gas known as an accretion disk. This accretion disk is believed to give rise to two jets of material moving in opposite directions.

The astronomers observed R Aquarii's jets and found that they appear to have rotated in the 13 years that have elapsed since the VLA first observed R Aquarii in 1982. "R Aquarii is the nearest known symbiotic star system," adds Pedelty, "and by continuing to watch it evolve we hope to understand in detail how the motion of the jet material is related to the motion of the two stars around each other."

This research is funded by NASA. The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.

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