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? 
 A: The 'input' parameters for stellar evolution are (*1): mass, binarity, metallicity (a broad term for initial chemical composition), spin, magnetic fields ... etc.  Based on these parameters, stars seem to evolve in a very regular way, first burning hydrogen in their core, then i) burning hydrogen in shells outside of a helium core, ii) burning heavier elements in the core (e.g. helium into heavier elements) or iii) stop burning altogether and transition into a remnant state like a white/brown dwarf.  Which of these paths they follow depends on their initial configuration (mostly their mass).  The type of evolution they undergo then determines their chemical evolution.
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.

*1: I've put these in order of their significance (as we understand it today) in determining how they evolve.  i.e. mass is the most important parameter, and so on.
