Confused about Metallicity Measurement in Milky Way

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SUMMARY

The metallicity of the Milky Way is quantified as z = 0.02, representing the mass fraction of elements heavier than hydrogen and helium. In astrophysics, "metals" include elements like carbon and iron, which are considered metals in this context. Metallicity is calculated as the ratio of metal mass to total mass, confirming that z is indeed a mass fraction rather than a number fraction.

PREREQUISITES
  • Understanding of astrophysical terminology, specifically "metallicity"
  • Familiarity with mass fractions in scientific measurements
  • Basic knowledge of the composition of celestial bodies
  • Awareness of the definitions of hydrogen and helium in astrophysics
NEXT STEPS
  • Research the concept of metallicity in different galaxies
  • Learn about the methods used to measure metallicity in stars
  • Explore the role of metallicity in stellar evolution
  • Study the implications of metallicity on galaxy formation and development
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Astronomers, astrophysics students, and anyone interested in the chemical composition of galaxies and their evolution.

malawi_glenn
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Hi!

I am reading text in metal abundances, for example one of my books states that the metallicity of the milky way is:

z = 0.02

etc.

Is that mass or number fraction? I have searched in all my books and google a bit but can't seem to find an answer :S

Help
 
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Metallicity is defined as the proportion of mass in an object that is not hydrogen or helium - could be carbon, iron, whatever else. Metals in this case are not the metallic elements as we think of the term. Carbon is a metal in this case, for example.

It is the metal mass / total mass

It's a fraction.
 
Great thanx!

I know all the other stuff you wrote, was just unsure if z is number or mass ratio.
 

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