Impact of instrumental systematic errors on fine-structure constant measurements with quasar spectra

We present a new ‘supercalibration’ technique for measuring systematic distortions in the wavelength scales of high-resolution spectrographs. By comparing spectra of ‘solar twin’ stars or asteroids with a reference laboratory solar spectrum, distortions in the standard thorium–argon calibration can be tracked with ∼10 m s−1 precision over the entire optical wavelength range on scales of both echel...