stellar populations

stellar populations,

two broadly contrasting distributions of star types that are characteristic of different parts of a galaxygalaxy,
large aggregation of stars, gas, dust, and usually dark matter, typically containing billions of stars. Recognition that galaxies are independent star systems outside the Milky Way came from a study of the Andromeda Galaxy (1926–29) by Edwin P.
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. Population I stars are young, recently formed stars, whereas population II stars are old and highly evolved. Population II stars are formed early in the history of the galaxy from pure hydrogen with an admixture of primordial helium. Because massive blue-white giants burn their nuclear fuel quickly and therefore have lifetimes of only a few million years, no stars of this type are found in population II. The most luminous population II stars are red giants. Population I stars, of which the sun is typical, are young stars that still lie mostly on the main sequence of the Hertzsprung-Russell diagramHertzsprung-Russell diagram
[for Ejnar Hertzsprung and H. N. Russell], graph showing the luminosity of a star as a function of its surface temperature. The luminosity, or absolute magnitude, increases upwards on the vertical axis; the temperature (or some temperature-dependent
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. The most luminous population I stars are blue giants. Because they are second-generation stars formed from the debris of exploded population II stars, population I stars have a considerable content of heavy elements that were created by nucleosynthesisnucleosynthesis
or nucleogenesis,
in astronomy, production of all the chemical elements from the simplest element, hydrogen, by thermonuclear reactions within stars, supernovas, and in the big bang at the beginning of the universe (see nucleus; nuclear energy).
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 in the interiors of the earlier stars. Population I and population II stars are both found in the spiral galaxies. Population I stars are located in the disk singly and in galactic, or open, star clustersstar cluster,
a group of stars near each other in space and resembling each other in certain characteristics that suggest a common origin for the group. Stars in the same cluster move at the same rate and in the same direction.
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. They are particularly concentrated in the interstellar dust of the spiral arms, where new stars are continually being formed. The very brightest population I stars are not distributed at random, but are grouped in loose associations of several hundred stars that partake in the general galactic rotation and are believed to have a common origin. Population II stars are found both in the spiral arms and in the gas-free and dust-free regions of the spiral galaxies, i.e., the nucleus and the halo of high-velocity stars and globular clusters that surround the disk of the galaxy. Irregular galaxies are predominantly, or sometimes exclusively, composed of population I stars. Elliptical galaxies, which lack spiral arms, are composed almost entirely of population II stars. The categories population I and population II were first introduced by Walter Baade as a result of his studies of the Andromeda GalaxyAndromeda Galaxy,
cataloged as M31 and NGC 224, the closest large galaxy to the Milky Way and the only one visible to the naked eye in the Northern Hemisphere. It is also known as the Great Nebula in Andromeda. It is 2.
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.
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stellar populations

See population I, population II.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
"These gargantuan galaxies are invisible in optical wavelengths so it's extremely hard to do spectroscopy, a way to investigate stellar populations and chemical composition of galaxies.
Dwarf spheroidal galaxies are defined by their small size, low-luminosity, lack of dust and old stellar populations The international team of astronomers that carried out this study consists of researchers from University of California Los Angeles, University of Bonn in Germany and Universite de Montreal in Canada, among others.
Stellar Populations and the Distance Scale: A Conference in Honor of Jeremy Mould
Previous studies had often compared the collective colors of stars in a globular cluster to models of stellar populations with known ages and compositions.
The finding not just reveals old stellar populations in the cosmos might be less ancient than previously thought but also changes our understanding of galactic formation and evolution.
The Subaru Telescope revealed that these dark galaxies contain old stellar populations and shows a spatial distribution similar to those of other brighter galaxies in the Coma Cluster.
To determine the mass and size of planets found around other stars or to date stellar populations in order to limit the number of cosmological models, among other things, it is essential to know what goes on inside a star.
It is also possible to compare these gradients with the radial distributions from the stellar populations to study possible migration effects.
Old stellar populations; how to study the fossil record of galaxy formation.
I will highlight some important results from this survey, including the discovery of multiple stellar populations in some globular clusters, constraints on the three-dimensional orientation of the Sagittarius dwarf galaxy and the relative ages of the 65 clusters.
However, due to their closeness it has been possible to examine them in detail, and the range of stellar populations is greater than in a globular, showing evidence of star formation over an extended period, although none in recent times.