AST- 105 1st EditionLecture 13Outline of Last LectureI. The Luminosity of StarsII. Inverse Square Law for RadiationOutline of Current Lecture I. Stellar Temperature, Color, and Spectra Current Lecture I. Stellar Temperature, Color, and Spectraa. λ max = const/ T T λ max3000 K (cool) IR6000 K Visible12,000 K (hot) UVi. Hot stars emit more blue than red light, therefore, they appear as blue.ii. Cool stars emit more red than blue light, therefore, they appear as red.iii. Only hot stars emit much UV.b. Stellar Spectrai. Stellar Spectra- spectral classification based on absorbtion lines.ii. Spectral Sequence –O B A F G K M1. This is a surface temperature sequence – from hot to cold.iii. Sun is G star.iv. All stars have a similar H and He composition:1. 75% H23% He> or equal to 2% other v. The coolest stars (m) show molecules. 1. Molecules are broken up above about 4000
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