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Wavelength Calibration Sources |
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This page documents the wavelengths of light emitted by the spectral calibration lamps used at Xanadu Observatory. A box containing two lamp power supplies allows for any single lamp, or combination of any two lamps, to be used. A fiber optic cable transmits the light directly into the SGS body, bypassing the slit. During lamp calibration frame exposures, the light path to the tracking CCD is blocked to avoid contamination of the images by other light sources. Hydrogen is especially useful for low resolution spectra because the Balmer series lines are prominent in either absorption or emission form in many targets. The Hydrogen tube emits a pinkish glow. The spectrum below was made with 60 second exposures (5x 60s at -15C, dark subtracted and median combined, not corrected for instrumental response).
The Mercury tube emits a bluish glow. It is very dangerous to look directly at the Mercury lamp because it has strong ultraviolet emissions. The spectrum below was made with 60 second exposures (5x60s at -15C, dark subtracted and median combined, not corrected for instrumental response).
The Neon tube emits a fairly strong orangish glow. The spectrum below was made with 60 second exposures (5x60s at -30C, dark subtracted and median combined, not corrected for instrumental response). There are no useable lines at the blue end of the spectrum.
The Krypton tube emits a faint light so longer exposures are needed. It has lines above 7000 Angstroms, so it is useful for spectra farther in the infrared. The spectrum below was made with 300 second exposures (5x300s at -30C, dark subtracted and median combined, not corrected for instrumental response).
An interesting historical side note - between 1960 and 1983, Krypton provided a standard for the definition of a meter. The meter was exactly 1,650,763.73 times the wavelength of the orange-red emission line of Krypton-86 in a vacuum. (A meter is now based on the path length of light in a vacuum)
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