Except for CNO elements, surface composition remains effectively unchanged over a stars life. Once a star forms, its chemical composition is mostly fixed for life. Metal content gives us a clue to the formation history of populations of stars. Massive Pop II stars go supernova and enrich the gas with metals. Low-mass Pop II stars are still around today.
Star formation stops early-on in the spheroid.
Disk Formation Metal-enriched gas settles into a rotating disk . Copyright 1998 Richard W. Pogge, All Rights Reserved.