Chemical Composition

Detailed spectral analysis also yields the chemical composition of the material (photosphere) that produced the absorption lines in a stellar spectrum. Most stars found in the Galaxy are chemically very similar to the Sun, approximately 74 percent hydrogen, 24 percent helium, and 2 percent all other elements (all elements heavier than helium are conventionally grouped together under the term metals). Stars do exist for which the heavy element fraction is larger ( metal‐rich stars) and others for which the heavy elements are deficient ( metal‐poor stars).