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Using the Rainbow Optics Star Spectroscope for Visual Observing

Using the Rainbow Optics Star Spectroscope for Visual Observing. Paul Bakke. Items to discuss:. How Rainbow Optics Star Spectroscope works for visual observing Optics used Objects observed First attempts using a camera with the Rainbow Optics Star Spectroscope. Standard eyepiece.

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Using the Rainbow Optics Star Spectroscope for Visual Observing

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  1. Using the Rainbow Optics Star Spectroscope for Visual Observing Paul Bakke

  2. Items to discuss: • How Rainbow Optics Star Spectroscope works for visual observing • Optics used • Objects observed • First attempts using a camera with the Rainbow Optics Star Spectroscope

  3. Standard eyepiece Diffraction grating cell Cylindrical lens Grating cell mounted to eyepiece

  4. Optical Considerations • Spectrum width proportional to Exit Pupil • Best: 2 to 3 mm (useful range 1.5 to 4 mm) • Spectrum length controlled by: • Eyepiece magnification • Distance from grating to eyepiece lens Exit Pupil = Eyepiece Focal length Telescope f-ratio Wider spectrum Longer eyepiece focal length Shorter spectrum

  5. Increases length or “dispersion” of spectrum Grating mounted to star diagonal

  6. My setup: 10-inch, f = 10 SCT 25 mm eyepiece

  7. Photo taken with hand-held Canon Power Shot at ¼ sec, f3.5, 1600 ISO

  8. Source: Jack Martin, London, England 12-inch Dobsonian with Rainbow Optics Star Spectroscope (2-piece model) Photo adapted from http://www.starspectroscope.com/

  9. Method: • Center spectrum in field of view • Turn off siderial drive • Take “long” exposure photo (< 30 sec.), just enough to “smear” the image • Rotate and crop using software

  10. Paint Shop Pro Bonus: Use graphics software to make intensity vs. color histogram

  11. What to observe • First-magnitude stars (using cylindrical lens) • Main-sequence (class V) stars are best • Giants & supergiants have less prominent absorption lines, • Cooler spectral types are good even at larger luminosity class • Spectacular: Vega (A0 V), Sirius (A1 V), Betelguese (M2 I)

  12. Absorption lines • Hot (type A, B) stars: • Hydrogen beta, gamma (blue) are easy • Hydrogen alpha (red), delta (violet) are difficult • In type G & cooler stars: G (blue – CH molecule), D (orange – Na), b (green- Mg) • Molecular bands (TiO) in M stars

  13. More challenging • Wolf-Rayet stars (type WN, WC) • Emission lines (blue) • HD 192163 in Cygnus (illuminates Crescent Nebula, NGC 6888), mag. 7.7, type WN6 • HD 192641 in Cygnus, mag. 8.2, type WC7 • Fact: ~½ of all Wolf-Rayet stars brighter than magnitude 9 are in Cygnus!

  14. More challenging • Carbon stars: absorption bands in blue & violet due to carbon molecules • Y Canum Venaticorum (“La Superba”) • U Hydrae • 19 Piscium

  15. Rainbow Optics Star Spectroscope • Spectroscopy at its most inexpensive & “low tech” • Pleasure of visual astronomy • Simple photographic possibilities • Activities in light-polluted or moonlit sky

  16. HAVE FUN!

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