Laboratory wavelengths for cosmological constraints on varying fundamental constants

Abstract

Cosmological investigations, using high-redshift quasi-stellar object (QSO) absorption spectra, of possible variations of the fine-structure constant (α) require very accurate laboratory wavelengths for a number of resonance transitions from several different species. A change in α could be detected as a shift in the wavelengths of atomic transitions in the QSO systems and to accurately determine the values of such shifts it is essential that the laboratory rest wavelengths are known to a high degree of accuracy and precision. The present status of such laboratory wavelengths is discussed with emphasis on our recent study including laboratory wavelengths and wavenumbers of ultraviolet (UV) resonance lines from seven species, measured using the UV high-resolution Fourier transform spectrometer in Lund. The high relative accuracy of the wavenumbers has been obtained by the use of a composite hollow-cathode light source, which enables the spectra of the different species to be recorded simultaneously and thereby minimizes the effects from several steps of calibration. Much emphasis has been put on investigations of possible wavenumber shifts from line structure and self-absorption as well as pressure shifts and calibration effects. The absolute as well as the relative wavenumber accuracy is discussed and the wavenumbers are compared with values from other investigations.