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Stellar Spectra

Stellar Spectra. Ay16 Lecture 2 Feb 5, 2008. The Nearest Star. SOHO UV Image. What is a Spectrum. The Atmospheres of stars. Spectral Lines & Quantum Mechanics (the Bohr atom) Ionization Spectral Types The Hertzsprung-Russell Diagram (intro to the evolution of stars).

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Stellar Spectra

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  1. Stellar Spectra Ay16 Lecture 2 Feb 5, 2008

  2. The Nearest Star SOHO UV Image

  3. What is a Spectrum. The Atmospheres of stars. Spectral Lines & Quantum Mechanics (the Bohr atom) Ionization Spectral Types The Hertzsprung-Russell Diagram (intro to the evolution of stars)

  4. Diffraction/Refraction Grating diffracts Prism refracts

  5. The Solar Spectrum Fraunhofer Lines in the spectrum of the Sun

  6. Fraunhofer Lines in the Solar Spectrum (~1817) Designation Wavelength Origin A 759.4 nm terrestrial oxygen B 686.7 terrestrial oxygen C 656.3 hydrogen (H alpha) D 589.0 neutral sodium (Na I) E 527.0 neutral iron (Fe I) F 486.1 hydrogen (H beta) G 430.3 metal blend H 396.8 ionized Calcium (Ca II) K 393.4 ionized Calcium (Ca II)

  7. Where do these features come from? Blackbody Emission by hot gas Absorption by cold gas in front of a hot source

  8. The Bohr Atom

  9. Hydrogen Atom Energy Levels

  10. Hydrogen Ionization Fraction

  11. IONIZATION ENERGIES (in electron volts = eV) Atom 1st 2nd 3rd 4th 5th Hydrogen H 13.60 Helium He 24.59 54.42 Lithium Li 5.39 75.64 122.45 Beryllium Be 9.32 18.21 153.90 217.72 Boron B 8.30 25.15 37.93 259.38 340.23 Carbon C 11.26 24.38 47.89 64.49 392.09 Nitrogen N 14.53 29.60 47.45 77.47 97.89 Oxygen O 13.62 35.12 54.94 77.41 113.90 Fluorine F 17.42 34.97 62.70 87.14 114.24 Neon Ne 21.56 40.96 63.45 97.12 126.21 Sodium Na 5.14 47.29 71.62 98.91 138.40 Magnesium Mg 7.65 15.04 80.14 109.27 141.27 Aluminum Al 5.99 18.83 28.45 119.99 153.83

  12. Ionization Energies

  13. Stellar Spectral Classification • Spectroscopy (photographic!) started in the late 19th century. • Classifiers originally arranged them alphabetically, A-O • A. J. Cannon figured out the right order from 200,000 objective prism spectra • O B A F G K M • And astronomers realized it was a well defined sequence in line strength.

  14. Digital spectral atlas (the modern version of the photographic atlas!)

  15. Hertzsprung-Russell Diagram Multicolor photography --- Blue and Visual Plates allowed “colors” Objective Prism Spectra Realization that Spectral Type related to Color related to Surface Temperature

  16. Hipparcos HR Diagram 4907 nearby stars with distances to < 5%.

  17. HR Diagram in Luminosity vs Temperature

  18. Solar Spectrum NOAO Atlas, N. Sharp

  19. Hydrogen Atom Energy Levels

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