Spectra of Different Luminosity Classes
Presence of different lines determined by Spectral Class(temperature)
Width ofindividual lines determined by Luminosity Class
�Pressure broadening�:
High density (so high pressure) frequent atomic collisions
Energy levels shifted by 2nd nearby atombroad 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