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Stellar Spectra Ay16 Lecture 2 Feb 5, 2008. The Nearest Star SOHO UV Image.

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Presentation on theme: "Stellar Spectra Ay16 Lecture 2 Feb 5, 2008. The Nearest Star SOHO UV Image."— Presentation transcript:

1 Stellar Spectra Ay16 Lecture 2 Feb 5, 2008

2 The Nearest Star SOHO UV Image

3 1.What is a Spectrum. 2.The Atmospheres of stars. 3.Spectral Lines & Quantum Mechanics (the Bohr atom) 4.Ionization 5.Spectral Types 6.The Hertzsprung-Russell Diagram (intro to the evolution of stars)

4 Diffraction/Refraction Prism refracts Grating diffracts

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)

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

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11 The Bohr Atom

12 Hydrogen Atom Energy Levels

13 Hydrogen Ionization Fraction

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15 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

16 Ionization Energies

17 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.

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19 Digital spectral atlas (the modern version of the photographic atlas!)

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21 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

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

24 HR Diagram in Luminosity vs Temperature

25 Solar Spectrum NOAO Atlas, N. Sharp

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27 Hydrogen Atom Energy Levels

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