ZERO-AGE MAIN SEQUENCE (ZAMS) - Region on the Hertzsprung-Russell diagram, as predicted by theoretical models, where stars are located at the onset of nuclear hydrogen burning in their cores.
Zero-Age Main Sequence
The position on the H-R diagram for stars which have attained hydrostatic equilibrium and have started hydrogen burning in their cores, ...
Zero-Age Main Sequence (ZAMS)
The locus in the H-R- diagram where stars first reach stability as hydrogen burning stars.
Zodiac ...
zero-age main sequence The region on the H-R diagram, as predicted by theoretical models, where stars are located at the onset of nuclear burning in their cores.
zero-age main sequence (ZAMS) - (n.)
The main sequence in the H-R diagram formed by stars that have just begun their hydrogen-burning life- times, and have not yet converted any significant fraction of their core mass into helium.
Cluster Ages and Zero-Age Main Sequence
Star clusters are particularly important because they allow astronomers to check models of stellar evolution and the ages of stars. Let us look firstly at open clusters to understand why this is so.
The Zero-Age Main Sequence (or ZAMS) is shown - it is the green line. This is only a theoretical location on the H-R diagram and is used to show the likely location where a newly formed star would be found before it has burned any hydrogen.
You must model the main sequence evolution to get back to the Zero-Age Main Sequence. This method assumes that all Zero-Age main sequence stars of a given temperature (and, hence, mass) start at the same luminosity.
Moreover, evolutionary theory shows that the star is not a subgiant at all, but is near the "zero-age main sequence," that is, it is very young true dwarf that is just starting to fuse its internal hydrogen into helium.
Aside from the additional hydrogen-burning layer, a horizontal branch star is somewhat like a zero-age main sequence star in that it will continue to evolve until it exhausts its supply of helium.
This plot gives an example of the mass-luminosity relationship for zero-age main sequence stars. The mass and luminosity are relative to the present-day Sun.
A Schrödinger-type equation for even-parity perturbations on the Schwarzschild metric. [H76]
Zero-Age Main Sequence ...
Starting at zero-age main sequence, the proportion of helium in a star's core will steadily increase. As a consequence, in order to maintain the required rate of nuclear fusion at the core, the star will slowly increase in temperature and luminosity.
 See also: Main Sequence, Hydrogen, Distance, Mass, Sun
  
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