UCLA Astronomers Find Evidence of Planet Formation in the Sigma Herculis System

Press Release From: University of California Los Angeles
Posted: Monday, January 13, 2003

UCLA astronomers have discovered evidence that planet formation may have occurred or may be occurring around the binary system sigma Herculis.

The astronomers -- Christine Chen and Michael Jura, found that observations of outflowing gas from around sigma Herculis suggest the existence of a parent body reservoir that is sufficiently massive to form planets.

"There is a tremendous amount of material circulating around this star, and based on our observations, we believe that this material may be forming planets, or may have already formed planets," said Chen.

As light from the binary system passes through the disk, it is absorbed by atomic gases. Chen, a post-doctoral researcher at JPL, and Jura, professor of astronomy at UCLA, studied the signature that the gas imprints on the stellar spectra.

Sigma Herculis is located in the constellation Hercules about 300 light years from our sun. The two stars are separated by 7 Astronomical Units (AU), with the primary being about two and a half times as massive as our sun.

Sigma Herculis is young in astronomical terms-- about 140 million years old, compared to our Sun, which is 4.5 billion years old.

Chen and Jura observed sigma Herculis with the Far Ultraviolet Spectroscopic Explorer (FUSE), an Earth- orbiting ultraviolet telescope. Using FUSE, they found evidence for atomic gas around sigma Herculis which is outflowing from the circumstellar matter in a wind. They believe that atoms in the wind are generated by collisions between parent bodies and are blown out of the system by radiation pressure from the two stars. Some of these collisions lead to debris, even as there is growth into planets.

Other studies of Sigma Herculis by Sergio Fajardo-Acosta et al. in 1998, found that it possesses 300 Kelvin (80 F) dust, a relatively high temperature for such material. Given this high temperature, the grains may be as close as 20 AU from the hot luminous binary stars.

"We found that the circumstellar gas around sigma Herculis probably lies in an edge-on disk, which makes it possible to see the gas," said Chen. "Building on the earlier observations that identified dust, we were able to infer that collisions between large objects were the most likely source for the dust."

The discovery of atomic gas around sigma Herculis was first published in 1989 by Frederick Bruhweiler, Carol Grady et al.

Chen and Jura hope to refine their findings with ultraviolet observations of sigma Herculis using the Hubble Space Telescope.

"We hope to obtain higher resolution ultraviolet spectra of the system to study the detailed dynamics of the gas," Chen said.

The research by Chen and Jura is supported by funding from NASA.

[NOTE: A diagram supporting this release is available at (8KB)]

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