Metallicity | Wikipedia audio article
Channel: Subhajit Sahu
Date: 25/03/2019

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Metallicity


00:02:20 1 Common methods of calculation
00:02:56 1.1 Mass fraction
00:05:53 1.2 Chemical abundance ratios
00:09:31 1.3 Photometric colors
00:11:19 2 Metallicities in various astrophysical objects
00:11:31 2.1 Stars
00:11:39 2.1.1 Relationship between stellar metallicity and planets
00:13:01 2.2 HII regions
00:14:42 3 See also
00:15:14 4 References
00:15:37 5 Sources
00:18:17 (3727, 4959 and 5007) Å wavelengths, divided by the flux from the Hβ emission line at the rest frame λ



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SUMMARY
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In astronomy, metallicity is used to describe the abundance of elements present in an object that are heavier than hydrogen or helium. Most of the physical matter in the Universe is in the form of hydrogen and helium, so astronomers use the word "metals" as a convenient short term for "all elements except hydrogen and helium". This usage is distinct from the usual physical definition of a solid metal. For example, stars and nebulae with relatively high abundances of carbon, nitrogen, oxygen, and neon are called "metal-rich" in astrophysical terms, even though those elements are non-metals in chemistry.
The presence of heavier elements hails from stellar nucleosynthesis, the theory that the majority of elements heavier than hydrogen and helium in the Universe ("metals", hereafter) are formed in the cores of stars as they evolve. Over time, stellar winds and supernovae deposit the metals into the surrounding environment, enriching the interstellar medium and providing recycling materials for the birth of new stars. It follows that older generations of stars, which formed in the metal-poor early Universe, generally have lower metallicities than those of younger generations, which formed in a more metal-rich Universe.
Observed changes in the chemical abundances of different types of stars, based on the spectral peculiarities that were later attributed to metallicity, led astronomer Walter Baade in 1944 to propose the existence of two different populations of stars.
These became commonly known as Population I (metal-rich) and Population II (metal-poor) stars. A third stellar population was introduced in 1978, known as Population III stars. These extremely metal-poor stars were theorised to have been the "first-born" stars created in the Universe.