14
Stellar
Population and Galaxy Evolution
•“Metal”
abundance during time
–“Metals”
are elements heavier than He
–A
given star’s atmospheric abundance is approx. fixed at birth
–Interstellar
metal abundance grows with each new generation of stars
•Red
giants and supernova eject new heavy elements into interstellar gas
•Orbits
during time
–A
given star’s orbit is approx. fixed at birth – just plows through
gas
–Orbits
of gas clouds evolve with time since they can collide
–Orbits
get more circular and disk-like with time
From our text: Horizons, by Seeds