metallicity

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metallicity

(met-ă-liss -ă-tee) (metal abundance) Symbol: Z . The fraction by mass of metals in a star, cluster of stars, or in some other astronomical entity. Since metals are produced by nucleosynthesis in stars, the metallicity of an object or class of objects depends on when it was formed: objects of later origin in general have a higher metallicity. Metallicity is determined by photometry or high-resolution spectroscopy, and is usually expressed relative to solar metallicity (see cosmic abundance), and as the ratio of iron to hydrogen, Fe/H. See also population I, population II.
References in periodicals archive ?
Arcturus is an ancient Population II star, perhaps 10 billion years old, that just happens to be plunging through the Milky Way's disk, which is mostly made up of younger Population I objects.
If its existence is confirmed, perhaps this locally delayed generation of very-low-metallicity stars should be called Population 0, since Population I stars are metal-rich stars and Population II stars are moderately metal-poor.
The process of reionization analyzes simple analytical considerations and compares existing observations, while a further chapter describes some of the issues regarding the transition from Population III to Population II stars, as well as the constraints that can be derived from WMAP.
2 percent as much mass as its galaxy's central bulge--the galaxy's spherical or ellipsoidal concentration of old, yellow, Population II stars (S&T: October 2000, page 28).
Since dwarf galaxies are dominated by old, reddened Population II stars, Freeman points out, this result is not surprising.

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