Astronomical Thorium HCL - Th - Argon Fill Gas
Astronomical spectrographs are used for a variety of high-precision measurements, ranging from the discovery of low-mass exoplanets to the possible variation of fundamental constants, such as the fine structure constant or the proton-electron mass ratio.
These works require excellent wavelength calibration sources and a detailed understanding of the associated uncertainties and systematics. In the era of extremely large telescopes, it is often the accuracy of the calibration source, not the intrinsic photon noise, that limits the achievable precision. Furthermore, the science goals of future extremely large telescopes will require very high precision calibration sources.
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