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

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
http://www.astro.ucla.edu/~cchen/images/parentbodies.gif (8KB)]