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Chemical evo of Galax - Coggle Diagram

- - - - Y = mass fraction of He
      - Z = mass fraction of others
      - X = mass fraction of H
    - - C,O,Ne,Mg,Si
      - synthesized via alpha process
    - - \( [\alpha / H]\)
  - - - Line rations
        
        senstive to density
        
        to temp
        
        different ionisation stages of the same element
        
        hard to detect due to high sensitivity
    - - R23 = \( \log_{10}{(O^+ + O^{++}/h\beta)}\)
      - 12 + log(O/H) ~ (8.533 +- 0.012) - (0.214 +- 0.012) x O3N2
      - \( O3N2 = \log(\frac{O^{++}}{H\eta})-\log(\frac{N^+}{H\alpha}) \)
    - - Measure absorption line
      - Some of the absorption is from MW
      - Also, isochrone fit and SSP fitting
  - - - Current mixture of elements
      - ISM enriched
    - - elements were in the ISM when stars were born
    - - Challenge is how much higher
- - - - They are way more compliated that the models
  - - - Progenitors lived short
      - More Mg less Fe
    - - More Fe
      - start after SF finished
      - delay 10^8-9
      - Contains in gas phase not stars
    - - Processes Mix together for SN II and SN Ia
      - [Mg/Fe] is smaller because Fe is higher
    - - Early stars
        
        more alpha
        
        less Fe
      - MW has to types:
        
        Old petal poor, high alpha
        
        Young metal rich, low alpha
- - - - 2 more assump
        
        ((\Psi(t) = pg(t))) means proportional to gas mass
        
        R ~ 0
      - \( \frac{dZ}{dt} = yp \Rightarrow Z(t) = Z_0 +ypt \)