RAS: A sparkling zirconium star

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bystander
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RAS: A sparkling zirconium star

Post by bystander » Wed Dec 08, 2010 10:28 pm

A sparkling zirconium star
Armagh Observatory | 06 Dec 2010
A team of astronomers led by graduate student Naslim and her supervisor Dr Simon Jeffery from Armagh Observatory in Northern Ireland has found the most zirconium-rich star ever discovered. Zirconium, the material used by jewellers to make false diamonds, glitters in clouds above the star’s surface. The scientists publish their results in the journal Monthly Notices of the Royal Astronomical Society.

The team made the discovery while looking for chemical clues that explain why a small group of stars reaching the end of their lives, known as helium-rich hot subdwarfs, have much less hydrogen on their surfaces than other similar stars. Using data obtained with the Anglo-Australian Telescope at the Siding Spring Observatory in New South Wales, the team looked at the evolved star LS IV-14 116, 2000 light years from the Sun in the direction of the border between the constellations of Capricornus and Aquarius.

The scientists used the telescope instruments to disperse the light of the star into a spectrum. Different elements and molecules give rise to characteristic patterns in stellar spectra, allowing Earth-based scientists to determine the composition of stars and other objects.

As expected, the spectrum of LS IV-14 116 had the usual lines arising from more common elements, but other strong lines were less easy to identify. A careful study showed four of these lines were due to a form of zirconium that only exists at temperatures above 20,000 degrees Celsius and had never previously been found in an astronomical spectrum.

Team member Prof. Alan Hibbert, from Queen's University Belfast, computed a model of the zirconium atom to predict the expected line strengths. With this information, the team measured the zirconium abundance in LS IV -14 116 to be ten thousand times as common as in the Sun (meaning that one atom in every two hundred thousand is zirconium rather than one in two billion). Further work showed the remaining unidentified lines to come from strontium, germanium and yttrium. Again, these elements were between one thousand and ten thousand times more abundant than normal.

In their paper the Armagh team argue that the unusual abundances in LS IV-14 116 are caused by the formation of cloud layers in the star's atmosphere – the only part of a star that can be seen directly. High concentrations of certain elements, mainly metals heavier than calcium, build up in these clouds but the same elements are scarce in layers above and below, meaning that their overall abundance is near normal. Dr Natalie Behara, now at the Université Libre de Bruxelles, calculated models of the star's atmosphere. This may well have a dramatic appearance, with many thin cloud layers, each due to a different metal.

The team also suggests that the star is shrinking from being a bright cool giant to a faint hot subdwarf. As the star shrinks, different elements sink down or float up in the atmosphere to a region where they become highly visible, making the apparent composition very sensitive to the star's recent history.

Most stars like the Sun have about ten zirconium atoms for every million silicon atoms. LS IV-14 116 has two million zirconium atoms for every one million silicon atoms. It is estimated that the zirconium layer seen in LS IV-14 116 would weigh about four billion tonnes or 4,000 times the world's annual production of zirconium.

Describing the new results, Dr Simon Jeffery said "It was very exciting to discover these completely new chemical signatures in our data. The peculiar abundances measured in this star, and hopefully in others, offer a new tool to explore a stage of stellar evolution which is extremely difficult to observe directly." Naslim reports "The huge excess of zirconium was a complete surprise. We had no reason to think this star to be more peculiar than any other faint blue star discovered so far."
An extremely peculiar hot subdwarf with a ten-thousand-fold excess of zirconium, yttrium, and strontium - Naslim N et al
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neufer
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Zircon stenches beyond owl's Kant troll

Post by neufer » Wed Dec 08, 2010 11:01 pm

http://en.wikipedia.org/wiki/Zirconium wrote:
<<Zirconium is a chemical element with the symbol Zr and atomic number 40. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium. The zirconium-containing mineral zircon, or its variations (jargoon, hyacinth, jacinth, ligure), were mentioned in biblical writings. The mineral was not known to contain a new element until 1789, when Klaproth analyzed a jargoon from the island of Ceylon (now Sri Lanka) in the Indian Ocean. He named the new element Zirkonerde (zirconia). Humphry Davy attempted to isolate this new element in 1808 through electrolysis, but failed. Zirconium (from Syriac ܙܐܪܓܥܢܥ zargono, meaning "gold like") was first isolated in an impure form in 1824 by Berzelius by heating a mixture of potassium and potassium-zirconium fluoride in a small decomposition process conducted in an iron tube.

Zirconium is relatively abundant in S-type stars, and it has been detected in the sun and in meteorites. Lunar rock samples brought back from several Apollo program missions to the moon have a quite high zirconium oxide content relative to terrestrial rocks.

Because of zirconium's excellent resistance to corrosion, it is often used as an alloying agent in materials that are exposed to corrosive agents, such as surgical appliances, explosive primers, vacuum tube getters and filaments. Zirconium dioxide (ZrO2) is used in laboratory crucibles, metallurgical furnaces, as a refractory material, and it can be sintered into a ceramic knife. Zircon (ZrSiO4) is cut into gemstones for use in jewelry. Zirconium carbonate (3ZrO2·CO2·H2O) was used in lotions to treat poison ivy, but this was discontinued because it occasionally caused bad skin reactions.

Ninety percent of all zirconium produced is used in nuclear reactors (in the form of zircaloys) because of its low neutron-capture cross-section and resistance to corrosion. Zirconium alloys are used in space vehicle parts for their resistance to heat, an important quality given the extreme heat associated with atmospheric reentry. Zirconium is also a component in some abrasives, such as grinding wheels and sandpaper.

High temperature parts such as combustors, blades and vanes in modern jet engines and stationary gas turbines are to an ever increasing extent being protected by thin ceramic layers which reduce the metal temperatures below and keep them from undergoing extensive deformation which could possibly result in early failure. They are absolutely necessary for the most modern gas turbines which are driven to ever higher firing temperatures to produce more electricity at less CO2. These ceramic layers are usually composed by a mixture of zirconium and yttrium oxide.

Zirconium has no known biological role. Zirconium forms both inorganic and organometallic compounds such as zirconium dioxide and zirconocene dichloride, respectively. There are five naturally occurring isotopes, three of which are stable. Short-term exposure to zirconium powder causes minor irritation, and inhalation of zirconium compounds can cause skin and lung granulomas.>>
Art Neuendorffer

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