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MgII  means  Mg+  or  singly  ionized,  1e-­‐  missing  

Annie Jump Cannon

Antonia Maury

Cecilia Payne-Gaposchkin

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Spectral  Type  

Ho@er   Colder  

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Zöllner’s (Incorrect) Hypothesis

Evolution Early-type Late-type

But  the  terminology  stuck…  

Subdivisions of Spectral Type:

Letter & Number

B0 hotter than B9

B0-B5 “early B”

B5–B9 “late B”

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Luminosity Class / Morgan-Keenan-Kellmann (MKK) Class

Class Description Ia-0 Hypergiant Ia Bright supergiant Iab Normal supergiant Ib Subluminous supergiant II Bright giants III Normal giants IV Subgiant V Main-sequence (dwarf) star

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V

III

I

Brown Dwarfs (only burn 2H NOT pp chain)