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 eyepieceDiffraction grating cellCylindrical lensGrating cell mounted to eyepiece

Optical ConsiderationsSpectrum width proportional to Exit PupilBest: 2 to 3 mm (useful range 1.5 to 4 mm)Spectrum length controlled by:Eyepiece magnificationDistance from grating to eyepiece lensExit Pupil = Eyepiece Focal length Telescope f-ratioLonger eyepiece focal lengthShorter spectrumWider spectrum

Grating mounted to star diagonalIncreases length or dispersion of spectrum

My setup:10-inch, f = 10 SCT25 mm eyepiece

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

Source: Jack Martin, London, England12-inch Dobsonian with Rainbow Optics Star Spectroscope (2-piece model)Photo adapted from http://www.starspectroscope.com/

Method:Center spectrum in field of viewTurn off siderial driveTake long exposure photo (< 30 sec.), just enough to smear the imageRotate and crop using software

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

What to observeFirst-magnitude stars (using cylindrical lens)Main-sequence (class V) stars are bestGiants & 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 linesHot (type A, B) stars: Hydrogen beta, gamma (blue) are easyHydrogen alpha (red), delta (violet) are difficultIn type G & cooler stars: G (blue CH molecule), D (orange Na), b (green- Mg)Molecular bands (TiO) in M stars

More challengingWolf-Rayet stars (type WN, WC)Emission lines (blue)HD 192163 in Cygnus (illuminates Crescent Nebula, NGC 6888), mag. 7.7, type WN6HD 192641 in Cygnus, mag. 8.2, type WC7Fact: ~ of all Wolf-Rayet stars brighter than magnitude 9 are in Cygnus!

More challengingCarbon stars: absorption bands in blue & violet due to carbon moleculesY Canum Venaticorum (La Superba)U Hydrae19 Piscium

Rainbow Optics Star SpectroscopeSpectroscopy at its most inexpensive & low techPleasure of visual astronomySimple photographic possibilitiesActivities in light-polluted or moonlit sky

HAVEFUN!