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� |
Presence of different lines determined by Spectral Class� (temperature)
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Width of�
individual lines determined by Luminosity Class
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�Pressure broadening�:
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High density (so high pressure) frequent atomic collisions
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Energy levels shifted by 2nd
nearby atom� broad lines
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Main sequence stars are �high� density and pressure
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Supergiants are low density and pressure
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Something can cause a main sequence star to expand to a large
size
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to form a giant or supergiant
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