7
Spectra
of Different Luminosity Classes
•Presence of different lines determined by Spectral
Class (temperature)
•Width of
individual lines determined by Luminosity Class
•“Pressure broadening”:
•High density (so high pressure) Þfrequent atomic collisions
•Energy levels shifted by 2nd nearby atom Þbroad lines
•Main sequence stars are “high” density and
pressure
•Supergiants are low density and pressure
•Something can cause a main sequence star to expand to a
large size
to form a giant or supergiant
to form a giant or supergiant
From our text: Horizons, by Seeds