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Basic Concepts on Chemical Evolution

Basic Concepts on Chemical Evolution. Cesare Chiosi Department of Astronomy University of Padova, Italy. Aims. To understand the pattern of abundances in the solar system, in the solar vicinity,

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Basic Concepts on Chemical Evolution

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  1. Basic Concepts on Chemical Evolution Cesare Chiosi Department of Astronomy University of Padova, Italy

  2. Aims To understand the pattern of abundances in the solar system, in the solar vicinity, in the Halo, Bulge, and Disk of the Milky Way, in external galaxies of different morplogical type, and finally in the Universe as a whole. An easy and difficult task at the same time!

  3. Abundances Standard abundances in the solar system and solar vicinity (inside 0.5 Kpc radius) provide the richest information. Detailed compilations are available (Cameron, Anders & Grevesse….). Surprisingly abundances are fairly homogenous going from one site to another. The Cosmic Soupe tastes the same in all restaurants!! With obvious differences. Why? Need to know the amount of mass (total and in gas and stars) in the solar vicinity. highly controversial, say total 70 Mo /pc^2 (from dynamics), stars 25 Mo/pc^2, gas 6 Mo/pc^2

  4. An old compilation but still…. Abundances are the relative number of atoms, gradients in dlogX/dR (R in kpc)

  5. Abundance ratios (neglect the lines) a-enhancement problem

  6. Metallicity DistributionG-Dwarf problem In the Disk virtually no star of low metallicity. In the Halo the opposite

  7. Age-Metallicity relationship In reality the relationship is much more dispersed: at any age a large scatter in metallicity can be seen.

  8. Present-day and Initial Mass Functionin the Solar Vicinity The present day mass function is derived from the observed luminosity function

  9. Passing from PDMF to IMF

  10. Popular IMFs Salpeter Larson, Chabrier x and a positive numbers Other, more or less equivalent formulations have been proposed over the years

  11. Need an assumption for Y(t)

  12. Simple Models Assumptions: Initial conditions Closure of the system: infall, outflow, radial flow, galactic winds Star formation rate Y(t) Chemical Yields Mixing Let ST, Sg, Ss be the surface mass densities (or masses in general) of total baryonic matter, gas, and stars respectively ………

  13. Basic Equations

  14. Instantaneous recycling

  15. … and that for abundances… Yi is the Key Quantity to be derived from stellar nucleosynthesis theory The equation for gas becomes…

  16. Close-Box Model Primary versus secondary elements………………… In many circumstances, this type of solution is not particularly satisfactory when compared to observational data Particular solutions

  17. Particular solutions Open Model The abundances tend to the Yield This type of model is often in better agreement with the observational data, e.g. the G-dwarf Problem in the Solar Vicinity

  18. Most popular model Predicts the right temporal dependence for Y(t) to explain G-Dwarf (Chiosi, 1980)

  19. The Chemical Yields: prescription The chemical yields are based on the state-of-the-art of stellar evolution and stellar nucleasynthesis theory. Important parameters and quantities to remember are MHe, Mco, Mr, and Mej (this latter for each elemental species)

  20. Prescription 1 (single stars)

  21. Prescription 2 (single stars)

  22. Prescription 3 (single stars)

  23. Prescription 4 (binary stars)

  24. Prescription 5 (binary stars)

  25. Prescription 6 (binary stars)

  26. Prescription 7 (final remarks)

  27. Structure Diagrams

  28. Element by element…..

  29. Element by element Is this theory successful ? Yes

  30. Results: O/Fe

  31. Results: alpha/Fe

  32. Results: C/Fe

  33. Results: N/Fe

  34. Remarks • It explains • G-Dwarf problem • Age-Metallicity • Gross chemical features of galaxies of different morphological type • It has been used in many different contexts and environments

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