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From: "Jay  P Hailey" 
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----- Original Message -----
From: "Frank Gasperik" 
To: 
Sent: Friday, July 25, 2003 2:08 AM Subject: Stars Rich In Heavy Metals
Tend To Harbor Planets


>
> This is INTERESTING! (Raised right Eyebrow)
>
> Frank Gasperik
>
> Source:  http://www.berkeley.edu/
>
> Date: 2003-07-24
>
> Stars Rich In Heavy Metals Tend To Harbor Planets
>
> Sydney, Australia - A comparison of 754 nearby stars like our sun - some
> with planets and some without - shows definitively that the more iron and
> other metals there are in a star, the greater the chance it has a
companion
> planet.
>
> "Astronomers have been saying that only 5 percent of stars have planets,
> but that's not a very precise assessment," said Debra Fischer, a research
> astronomer at the University of California, Berkeley. "We now know that
> stars which are abundant in heavy metals are five times more likely to
> harbor orbiting planets than are stars deficient in metals. If you look at
> the metal-rich stars, 20 percent have planets. That's stunning."
>
> "The metals are the seeds from which planets form," added
colleague Jeff
> Valenti, an assistant astronomer at the Space Telescope Science Institute
> (STScI) in Baltimore, Md.
>
> Fischer will present details of the analysis by her and Valenti at 1:30
> p.m. Australian Eastern Standard Time (AEST) on Monday, July 21, at the
> International Astronomical Union meeting in Sydney, Australia.
>
> n and other elements heavier than helium - what astronomers lump together
> as "metals" - are created by fusion reactions inside stars
and sown into
> the interstellar medium by spectacular supernova explosions. Thus, while
> metals were extremely rare in the early history of the Milky Way galaxy,
> over time, each successive generation of stars became richer in these
> elements, increasing the chances of forming a planet.
>
> "Stars forming today are much more likely to have planets than early
> generations of stars," Valenti said. "It's a planetary baby
boom."
>
> As the number of extrasolar planets has grown - about 100 stars are now
> known to have planets - astronomers have noticed that stars rich in metals
> are more likely to harbor planets. A correlation between a star's
> "metalicity" - a measure of iron abundance in a star's outer
layer that is
> indicative of the abundance of many other elements, from nickel to silicon
> - had been suggested previously by astronomers Guillermo Gonzalez and Nuno
> Santos based on surveys of a few dozen planet-bearing stars.
>
> The new survey of metal abundances by Fischer and Valenti is the first to
> cover a statistically large sample of 61 stars with planets and 693 stars
> without planets. Their analysis provides the numbers that prove a
> correlation between metal abundance and planet formation.
>
> "People have looked already in fair detail at most of the stars with known
> planets, but they have basically ignored the hundreds of stars that don't
> seem to have planets. These under-appreciated stars provide the context
for
> understanding why planets form," said Valenti, who is an expert at
> determining the chemical composition of stars.
>
> The data show that stars like the sun, whose metal content is considered
> typical of stars in our neighborhood, have a 5 to 10 percent chance of
> having planets. Stars with three times more metal than the sun have a 20
> percent chance of harboring planets, while those with 1/3 the metal
content
> of the sun have about a 3 percent chance of having planets. The 29 most
> metal-poor stars in the sample, all with less than 1/3 the sun's metal
> abundance, had no planets.
>
> "These data suggest that there is a threshold metalicity, and thus not all
> stars in our galaxy have the same chance of forming planetary systems,"
> Fischer said. "Whether a star has planetary companions or not is a
> condition of its birth. Those with a larger initial allotment of metals
> have an advantage over those without, a trend we're now able to see
clearly
> with this new data."
>
> The two astronomers determined metal composition by analyzing 1,600
spectra
> from more than 1,000 stars before narrowing the analysis to 754 stars that
> had been observed long enough to rule a gas giant planet in or out. Some
of
> these stars have been observed for 15 years by Fischer, Geoffrey Marcy,
> professor of astronomy at UC Berkeley, and colleague Paul Butler, now at
> the Carnegie Institution of Washington, in their systematic search for
> extrasolar planets around nearby stars. All 754 stars were surveyed for
> more than two years, enough time to determine whether a close-in,
> Jupiter-size planet is present or not.
>
> Though the surfaces of stars contain many metals, the astronomers focused
> on five - iron, nickel, titanium, silicon and sodium. After four years of
> analysis, the astronomers were able to group the stars by metal
composition
> and determine the likelihood that stars of a certain composition have
> planets. With iron, for example, the stars were ranked relative to the
iron
> content of the sun, which is 0.0032%.
>
> "This is the most unbiased survey of its kind," Fischer
emphasized. "It is
> unique because all of the metal abundances were determined with the same
> technique and we analyzed all of the stars on our project with more than
> two years of data."
>
> Fischer said the new data suggest why metal-rich stars are likely to
> develop planetary systems as they form. The data are consistent with the
> hypothesis that heavier elements stick together easier, allowing dust,
> rocks and eventually planetary cores to form around newly ignited stars.
> Since the young star and the surrounding disk of dust and gas would have
> the same composition, the metal composition observed from the star
reflects
> the abundance of raw materials, including heavy metals, available in the
> disk to build planets. The data indicate a nearly linear relationship
> between amount of metals and the chance of harboring planets.
>
> "These results tell us why some of the stars in our Milky Way galaxy have
> planets while others do not," said Marcy. "The heavy metals must clump
> together to form rocks which themselves clump into the solid cores of
> planets."
>
> The research by Fischer and Valenti is supported by the National
> Aeronautics and Space Administration, the National Science Foundation, the
> Particle Physics and Astronomy Research Council (PPARC) in the United
> Kingdom, the Anglo-Australian Observatory, Sun Microsystems, the Keck
> Observatory and the University of California's Lick Observatories.
>
> A bar graph showing the relationship between stellar metal abundance and
> likelihood of planets is available at
> http://www.berkeley.edu/news/media/releases/2003/07/21_iron.pdf.
>
> Editor's Note: The original news release can be found here:
> http://www.berkeley.edu/news/media/releases/2003/07/21_stars.shtml
>
> This story has been adapted from a news release issued by University Of
> California - Berkeley.
>
>


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