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

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

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, f3.5, 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

Use graphics software to make intensity vs. color histogram 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 (A0 V), Sirius (A1 V), Betelguese (M2 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 (TiO) 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 WN6 HD 192641 in Cygnus, mag. 8.2, type WC7 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!