Confused about Metallicity Measurement in Milky Way

In summary, Metallicity is a measure of the proportion of mass in an object that is not hydrogen or helium. It includes elements such as carbon and iron and is calculated as metal mass divided by total mass. This means that z = 0.02 is a mass ratio, not a number ratio.
  • #1
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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  • #2
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 [tex] metal mass / total mass[/tex]

It's a fraction.
 
  • #3
Great thanx!

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

1. What is metallicity?

Metallicity refers to the abundance of elements heavier than hydrogen and helium in a celestial body or object. In astronomy, it is usually used to describe the amount of metals present in stars and galaxies.

2. Why is measuring metallicity important in the Milky Way?

Measuring metallicity in the Milky Way is important because it can provide valuable information about the formation and evolution of our galaxy. It can also help us understand the chemical composition of stars and their potential to host habitable planets.

3. How is metallicity measured in the Milky Way?

Metallicity in the Milky Way is typically measured using spectroscopy techniques. Spectroscopy involves analyzing the light emitted by stars and other celestial objects to determine the elements present and their relative abundance.

4. What is the unit of measurement for metallicity?

The unit of measurement for metallicity is often given as [Fe/H], which represents the logarithmic ratio of iron to hydrogen in a star or galaxy. This notation is commonly used in astronomy to describe metallicity levels.

5. How does metallicity vary in different parts of the Milky Way?

Metallicity can vary greatly in different parts of the Milky Way. Typically, the central regions of the galaxy have higher metallicity levels due to the presence of more massive and evolved stars. Outer regions, on the other hand, tend to have lower metallicity levels as they contain younger and less evolved stars.

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