Accurate laboratory ultraviolet wavelengths for quasar absorption-line constraints on varying fundamental constants

Abstract

The most precise method of investigating possible space–time variations of the fine‐structure constant, α≡ (1/ħc)(e2/4πε0), using high‐redshift quasar absorption lines is the many‐multiplet (MM) method. For reliable results this method requires very accurate relative laboratory wavelengths for a number of UV resonance transitions from several different ionic species. For this purpose laboratory wavelengths and wavenumbers of 23 UV lines from Mg i, Mg ii, Ti ii, Cr ii, Mn ii, Fe ii and Zn ii have been measured using high‐resolution Fourier transform (FT) spectrometry. The spectra of the different ions (except for one Fe ii line, one Mg i line and the Ti ii lines) are all measured simultaneously in the same FT spectrometry recording by using a composite hollow cathode as a light source. This decreases the relative uncertainties of all the wavelengths. In addition to any measurement uncertainty, the wavelength uncertainty is determined by that of the Ar ii calibration lines, by possible pressure shifts and by illumination effects. The absolute wavenumbers have uncertainties of typically ±0.001–±0.002 cm−1 (Δλ≈ 0.06–0.1 mÅ at 2500 Å), while the relative wavenumbers for strong, symmetric lines in the same spectral recording have uncertainties of ± 0.0005 cm−1 (Δλ≈ 0.03 mÅ at 2500 Å) or better, depending mostly on uncertainties in the line‐fitting procedure. This high relative precision greatly reduces the potential for systematic effects in the MM method, while the new Ti ii measurements now allow these transitions to be used in MM analyses.

Experimental Ca I oscillator strengths for the 4p–5s triplet

“…The wavenumbers of 24 Ar ii calibration lines were taken from Whaling et al (1995) in the wavenumber range 12469.2 to 21149.7 cm −1 (8017.5 to 4726.9 Å). A further discussion of wavenumber calibration and uncertainties can be found in Aldenius et al (2006).…”

A new measure of $\mathsf{\Delta\alpha/\alpha}$ at redshift $\mathsf{z = 1.84}$ from very high resolution spectra of Q 1101–264

“…The corresponding sensitivity coefficients are listed in Table 5 in Paper II. The rest frame wavelengths for some Fe ii transitions have been re-measured recently with higher accuracy by Aldenius et al (2006). For our present work we need two of them: 2382.7641 ± 0.0001 Å, and 2600.1722 ± 0.0001 Å.…”

High-Precision Measurements of Δα/αfrom QSO Absorption Spectra

“…It means that the relative change of the frequency ω 0 due to varying α is proportional to the so-called sensitivity coefficient Q = q/ω 0 [4]. The q-values for the resonance UV transitions in Fe ii are taken from [10], and their rest frame wavelengths -from [8,11].…”