<p>You cannot calculate the solar ration of <span class="math-container">$\mathrm{Fe/H}$</span> nor can you calculate the logarithmic ratio of iron to hydrogen for a star - both are entities you have to measure. So in order to calculate the relative metallicity of a star <span class="math-container">$[Fe/H]_\star$</span> in terms of solar metallicity <span class="math-container">$\log_{10}{\mathrm{Fe_0/H_0}}$</span> you also have to know the absolute metallicity of the star from the <em>number ratio</em> of its constituent atoms <span class="math-container">$\log_{10}{\mathrm{Fe_*/H_*}}$</span>.</p>
<p>Now, you are given the <em>weight ratio</em> of 20kg iron to 1000kg hydrogen. Convert the weight ratio into number ratios given the typical atomic weight of these two elements, plug in the number ratios in above equation and you are done (I will leave the calculation details to the interested reader; you are very likely assumed to lookup the solar values as well as necessary atomic properties).</p>

CC BY-SA 4.0
2022-06-13T13:27:32.047Z
2022-06-13T15:26:14.423Z
2022-06-13T15:26:14.423Z
planetmaker
<p>I want to know how to calculate star metallicity using only masses of metal and hydrogen of the star. I am attaching my working so far. I am not sure how to exactly calculate the log10(Fe/H) based on masses alone.
Also, please note I am not sure how the log10(Fe/H) of the Sun is obtained either. I just found the value online. So, explaining one will help explain the other, I guess.</p>
<p><a href="https://i.sstatic.net/6BV9L.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/6BV9L.jpg" alt="enter image description here" /></a>
Thanks!</p>

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2022-06-13T13:35:48.343Z
You would greatly increase the readability and accessability of your question, if you typed the formula as text using MathJax (kinda LaTeX format).
planetmaker
<star><mass><metallicity>
How to calculate metallicity of a star that is made of iron of 20kg and Hydrogen 1000 kg?
Jerome
# How to calculate metallicity of a star that is made of iron of 20kg and Hydrogen 1000 kg?

(Asked by: username_0 on 2022-06-13)

I want to know how to calculate star metallicity using only masses of metal and hydrogen of the star. I am attaching my working so far. I am not sure how to exactly calculate the log10(Fe/H) based on masses alone.
Also, please note I am not sure how the log10(Fe/H) of the Sun is obtained either. I just found the value online. So, explaining one will help explain the other, I guess.

[![enter image description here](https://i.sstatic.net/6BV9L.jpg)](https://i.sstatic.net/6BV9L.jpg)
Thanks!

**Tags:** star, mass, metallicity

> **Comments:**
> **username_1**: You would greatly increase the readability and accessability of your question, if you typed the formula as text using MathJax (kinda LaTeX format).  

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## 1 answers

### Answer by username_1 on 2022-06-13. Score: 4

You cannot calculate the solar ration of $\mathrm{Fe/H}$ nor can you calculate the logarithmic ratio of iron to hydrogen for a star - both are entities you have to measure. So in order to calculate the relative metallicity of a star $[Fe/H]\_\star$ in terms of solar metallicity $\log\_{10}{\mathrm{Fe\_0/H\_0}}$ you also have to know the absolute metallicity of the star from the *number ratio* of its constituent atoms $\log\_{10}{\mathrm{Fe\_\*/H\_\*}}$.

Now, you are given the *weight ratio* of 20kg iron to 1000kg hydrogen. Convert the weight ratio into number ratios given the typical atomic weight of these two elements, plug in the number ratios in above equation and you are done (I will leave the calculation details to the interested reader; you are very likely assumed to lookup the solar values as well as necessary atomic properties).


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