Using the Rainbow Optics Star Spectroscope for Visual

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

$Standard eyepiece Diffraction grating cell Cylindrical lens Grating cell mounted to eyepiece$

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

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 Longer eyepiece focal length Wider spectrum Shorter spectrum

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

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

Photo taken with hand-held Canon Power Shot at ¼ sec, f 3. 5, 1600 ISO

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

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

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

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 (A 0 V), Sirius (A 1 V), Betelguese (M 2 I)

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 (Ti. O) in M stars

More challenging Wolf-Rayet stars (type WN, WC) – Emission lines (blue) – HD 192163 in Cygnus (illuminates Crescent Nebula, NGC 6888), mag. 7. 7, type WN 6 – HD 192641 in Cygnus, mag. 8. 2, type WC 7 Fact: ~½ of all Wolf-Rayet stars brighter than magnitude 9 are in Cygnus!

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

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

HAVE FUN!