More than 40 nearby stars show excess infrared emission similar to that discovered last year around the star Vega (Alpha Lyrae), according to recently analyzed results from the Infrared Astronomical Satellite (IRAS) mission, joint project of the U.S., The Netherlands and the United Kingdom.
Vega (Alpha Lyrae) and later, Fomalhaut (Alpha Piscis Austrini) were each found to be orbited by solid material, probably in the form of small grains. The new discovery of dozens of other nearby stars sharing infrared characteristics similar to Vega and Fomalhaut suggests that stars orbited by solid material -- which may evolve into planets -- may occur ordinarily in our galaxy, the Milky Way.
Further study of the 40-some stars will be required, however, to determine if the excess infrared means that solid, orbiting material is present.
IRAS science team member Dr. Hartmut H. Aumann of NASA's JPL examined IRAS observations of 335 visually identified stars within 75 light years of Earth and found that more than 40 of them have infrared characteristics similar to those of Vega -- an excess of infrared radiation in the 25 to 100 micron-wavelength region of the spectrum.
Aumann emphasized that IRAS has not detected any individual planets around these stars.
He reported the new findings today at meeting of the American Astronomical Society in Baltimore, Md.
"The observational evidence that many dwarf stars show infrared excess similar to Vega is clear," Aumann said. "We are dealing with phenomenon shared by significant fraction of the dwarf stars in the neighborhood of the Sun" within our galaxy. "What is not clear and what requires lot more study is how to interpret what we are seeing," he added.
Besides orbiting solid material, the infrared excess around the stars could be due to any of several possibilities, including mass loss from the star or the presence of previously undetected cool stellar companion. While these mechanisms were ruled out in the case of Vega, additional study of each candidate star will be required to determine whether the excess comes from orbiting solid material.
Like Vega and Fomalhaut, the stars are relatively bright main sequence dwarfs. However, unlike those two A- type stars (hot, young, and luminous), most of the 40 stars are of the and G-type. This makes them more similar to the Sun, G-type dwarf star, in terms of luminosity, mass, and lifetime.
The actual number of stars within 75 light years which exhibit excess infrared emission is most likely significantly higher than the 40 observed, because large number of nearby stars are too faint to be detected by IRAS.
Studies of Vega and stars that share its infrared characteristics will help scientists to understand how planetary systems form and to determine which stars are likely to possess planetary systems in advanced stages of evolution.
Dust and debris-type materials are detected relatively easily by IRAS. Fully formed planets around stars are much more difficult to detect, however, because they have far smaller surface areas than shell or disk of particles. For an analagous reason, Saturn's moons are visually less apparent than its rings.
IRAS was launched into polar orbit by NASA Jan. 25, l983, from Vandenberg Air Force Base in California. The orbiting telescope mapped 98 percent of the sky during the l0- month mission, measuring the infrared emission and location of more than 250,000 stars, galaxies, clouds of dust and gas and other celestial objects.
IRAS is joint project of NASA, The Netherlands Space Agency (NIVR), and the United Kingdom's Science and Engineering Research Council. NASA's JPL is the managment center for the project.
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