Abstract

The metal absorption lines found in high resolution QSO spectra have been at the forefront of measurements of several fundamental dimensionless constants of nature. These measurements are made by comparing the relative wavelength spacings of absorption lines found of QSO spectra. The fine-structure constant (alpha) and the mass ratio of the proton to electron (mu) are two fundamental constants that have been measured to a relative precision of a few parts per million in the redshift range ~0.5—4.0. They thus require careful wavelength calibration.

The high resolution echelle spectrographs UVES and HIRES on the telescopes VLT and Keck (respectively) have provided the measurements resulting in evidence of a change in the value of alpha over cosmological time. Measurements of alpha in hundreds of absorption systems in a study combining data (153 measurements on VLT and 141 measurements on Keck), have led to a proposed spatial dipole across the sky (King, et al., 2012). My research has recently uncovered several long-range wavelength calibration distortions that have direct implications for alpha and mu measurements taken with each spectrograph. I will present some preliminary results on the effect that these systematic errors have on previously published results.