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A Spectrum: what it is and what it can tell us

A Spectrum: what it is and what it can tell us. Mary Lou West AAI, July 26, 2013. Our Theme. An alternation of experiment and theory (new equipment and new ideas) propels us to understand the world better and better. My Goal. T o show you some neat stuff,

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A Spectrum: what it is and what it can tell us

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  1. A Spectrum: what it is and what it can tell us Mary Lou West AAI, July 26, 2013

  2. Our Theme An alternation of experiment and theory (new equipment and new ideas) propels us to understand the world better and better.

  3. My Goal To show you some neat stuff, and to have you begin to understand it. Are you ready?

  4. Dispersion of white light by a glass prism Isaac Newton reversed the process in 1666.

  5. Astronomy became Astrophysics • We learned about the stars’ make-up and slow motions, opening up binary star orbits, exoplanets, orbits in galaxies, and cosmology. • We knew about the types of visible light, then we learned about other types of light.

  6. Infrared Light • William Herschel, February 1800 • Looking for good filters for the sun, to observe sunspots • Thermometer read hot below “red”

  7. Sunlight as white light, thin dark lines found In 1814 Joseph Fraunhofer invented the spectroscope to characterize types of glass more accurately. In the 1820’s he saw the thin dark lines in the solar spectrum.

  8. Wilhelm Wien • Explained how the color of a hot body depends on its temperature in 1893

  9. Colors of Stars

  10. Stefan-Boltzmann Law • 1879 Jozef Stefan and Ludwig Boltzmann • total energy/surface area of light emitted by a very hot solid object depends on the temperature of the object to the 4thpower • Wow!

  11. Spectrum of a hot gas Hydrogen Helium Neon

  12. Gas spectral lines • In the 1850’s Gustav Kirchoff and Robert Bunsen explained the dark Fraunhofer lines in the sun’s spectrum as absorption by the chemical elements, each one with a different “fingerprint”

  13. Spectrum portions Gamma Peg The Sun

  14. Spectra of Sun, Gam Peg

  15. Gamma Peg

  16. Calibration, hydrogen tube

  17. Spectral Classification • Annie Jump Cannon, one of Harvard’s “Computers” • Classified thousands of stars • System started ABC..O • But ended up as OBAFGKM

  18. Chemical Composition • Cecelia Payne modeled the stars • Found that they were mostly (70%) hydrogen • Very different from the Earth! • They are also 25% helium • There was only 5% for all the remaining chemical elements

  19. Emission Lines • There are hot dense gas clouds (M42) • There are dense winds around some stars (Wolf-Rayet stars) • There are planetary nebulae • There are supernova remnants

  20. Doppler Shift • Velocity: • blue-shifted means approaching Earth • Red-shifted means receding from Earth • The amount of color shift indicated the speed • Some speeds are 20% the speed of light, or more!

  21. Hubble’s Law of Cosmological Redshift

  22. Types of spectroscopes Sivo Star Analyzer 100 • Shelyak

  23. Star Analyzer 100 • The star image is the zero-order, so makes calibration easy • Unfortunately, the resolution is poor

  24. RSpec software

  25. Projects to Try In the Solar System • Velocities of the rings of Saturn, calculate the mass of Saturn itself • Comets, as tails grow • Asteroids, carbonaceous are farther out

  26. Atmospheres of jovian planets, especially ammonia at 643 nm in Jupiter but not Saturn.

  27. Projects with Stars • Examples of spectral types of stars • Wolf-Rayet stars, emission lines of dense hot gas thrown out. Clumpy? Periodic? • Colliding wind binaries, especially at periastron • Stars eclipsed by disks, clouds,… • Young T Tauri stars, formation of planets • Be stars with emission lines

  28. More projects with stars • Stars with variable lines, (Alioth) • Modeling with synthetic spectra • Stars with unusual elements, technicium, europium • Stars doing thermal pulses • Planetary nebulae • Novae • Supernovae

  29. Extragalactic Projects • Different types of galaxies • Velocity dispersion by line broadening • Rotation curves of galaxies • Quasars, red shift (3C 273, 16% c)

  30. Inspiration at the Meadowlands, yesterday

  31. Inspiration from articles • Field, Tom, Spectroscopy for Everyone, Sky and Telescope, Aug 2011, p 68 • Hattenbach, Jan, Deciphering Starlight, Sky and Telescope, Sep 2013, p 30 • Kannappan, Sheila, Fabricant, Daniel, Getting the Most from a CCD Spectrograph, Sky and Telescope, July 2000, p 125

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