# Compositions of stars at different stages

So I have been trying to find what stars chemical composition is depending on the stage and I have not found anything beyond the "average star" or our sun. For example out the sun and many others start off at 74% hydrogen,25% helium and 1% other heavy elements and within 5 billion years the chemical composition would be 70% hydrogen, 29% helium and 1% other heavy elements. How could I find the chemical composition of other types of stars such as red supergiants, red giants, blue supergiants, etc; And while doing so I can find out the beginning composition and ending composition with the time that has passed between that shift in the ratio?

• And while doing so I can find out the beginning composition and ending composition with the time that has passed between that shift in the ratio? Is it naive to say the answer to this is the same as you have in your post, the only difference initially is the mass , which determines the time taken to evolve to the stars ending composition, which is very broad in the scope of possible answers, given the wide range of outcomes observed? – user140606 Feb 10 '17 at 21:45
• @Countto10 not quite. The beginning composition is effectively an input parameter for stellar evolution, and does have an effect on how it evolves, and thus its end composition. – DilithiumMatrix Feb 10 '17 at 23:10

Attached is an image showing the chemical structure ('abundance profile') of a massive (15 $M_\odot$) star, right before it explodes as a thermonuclear ('core-collapse') supernova. You can see that the structure is very complex, and involves a large number of species, certainly not just hydrogen and helium. To calculate the structure or composition of stars, one must use numerical simulations---in particular, the standard code is called MESA, which can be downloaded here, and specifications can be found here. MESA was used to produce the solid lines in the attached figure.
• Very nice answer. What's up with the sudden changes in $\log X$ at around $m\sim1.72M_{\odot}$? – HDE 226868 Feb 16 '17 at 16:47