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Astrophysics and Space Science

, Volume 54, Issue 2, pp 453–466 | Cite as

Chemical evolution of the Galaxy at the initial rapid-collapse phase

  • R. Caimmi
Article

Abstract

Equations for the chemical evolution of the Galaxy are derived, accounting for (i) the dynamical evolution of the Galaxy (i.e. the collapse of the proto-galaxy), and (ii) either a variable mass-spectrum in the birth-rate stellar function of the type ℬ(m, t)=ψ(t)ϕ(m, t), or a constant mass-spectrum with variable lower mass limit for star birth:mmf=mmf(Z). Simple equations are adopted for the collapse of the proto-galaxy, accounting for the experimental data (i.e. axial ratio and major semi-axis) relative to the halo and to the disk, and best fitted for a rapid collapse; gas density is assumed to be always uniform. Numerical computations of several cases show that there is qualitative agreement with the experimental data relative to theZ(t) function when: (i) the mass-spectrum is nearly constant in time: ϕ(m, t)≈ϕ(m)=m−2.35; (ii) the efficiency ψ(t) ∝ ϱα is sufficiently high; moreover, the super metallic effect (SME) takes place for α greater than a given value (α≳1.5); (iii) the shorter the collapse timeTc, the more rapid is the initial increase of metallicity, the asymptotic value being left nearly unaltered. The theoretical present-day values of gas density and metallicity so obtained differ from the experimental values by a factor of 2 or 3. Leaving aside other possible explanations, such a discrepancy is within the range of the uncertainties concerning the amount of gas returned back into space by the decay of the stars. Our theoretical results are not in complete agreement with the observed data bearing on theNn(Z) function (Nn is the number of stars whose Main-Sequence lifetime is not less than the age of the Galaxy), while a hypothesis of star formation with different efficiencies in different zones of the Galaxy, and successive stellar mixing from zone to zone, is not inconsistent with such data.

Keywords

Experimental Data Numerical Computation Theoretical Result Dynamical Evolution Lower Mass 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© D. Reidel Publishing Company 1978

Authors and Affiliations

  • R. Caimmi
    • 1
  1. 1.Istituto di Astronomia dell'Università di PadovaPadovaItaly

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