Accurate laboratory wavelengths of some ultraviolet lines of Cr, Zn and Ni relevant to time variations of the fine structure constant

Abstract

The quality of astronomical spectroscopic data now available is so high that interpretation and analysis are often limited by the uncertainties of the laboratory data base. In particular, the limit with which space–time variations in the fine structure constant α can be constrained using quasar spectra depends on the availability of more accurate laboratory rest wavelengths. We recently measured some transitions in magnesium by high‐resolution Fourier transform spectroscopy for this purpose, and we now report measurements on some ultraviolet resonance lines of Zn ii (2062 and 2026 Å), Cr ii (2066, 2062 and 2056 Å) and Ni ii (1751, 1741, 1709 and 1703 Å). Apart from the last line, which is very weak, the uncertainty of these measurements is 0.002 cm−1 (0.08 må) for the lines around 2000 Å and 0.004 cm−1 (0.12 må) for the lines around 1700 Å.

COMPREHENSIVE OBSERVATIONS OF THE ULTRAVIOLET SPECTRUM AND IMPROVED ENERGY LEVELS FOR SINGLY IONIZED CHROMIUM (Cr II)

“…Agreement of our new results with the published results of Pickering et al (2000) and Aldenius (2009), given in the first two columns of Table 3, is satisfactory. Nave (2012) has proposed that the published measurements can be improved and their uncertainties reduced by making a small correction in their absolute calibration.…”

“…In recent years there has been particular interest in a handful of Cr ii absorption lines that are observed in the spectra of interstellar clouds along the line of sight toward quasars. Precise laboratory observations have been reported for these lines (Pickering et al 2000;Aldenius 2009) because of their application in studying a possible variation of the fine-structure constant (α) on cosmological timescales (Murphy et al 2003). For more general applications, however, the available data for Cr ii are often inadequate for quantitative interpretation of astronomical spectra.…”

Isotope shifts and relativistic shifts of Cr ii for the study ofαvariation in quasar absorption spectra

“…The experimental energies that we use for comparison are taken from the NIST database [27] (see also [28]). More recently, absolute frequencies were remeasured with very high accuracy for the lines seen in quasar absorption spectra specifically for the purpose of studying α variation [29]; however, such accuracy is unnecessary for the purpose of comparison with theory.…”

Probing the cosmological variation of the fine-structure constant: Results based on VLT-UVES sample

“…wavelength:-(L) Pickering et al (1998); (M) Griesmann & Kling (2002); (P) Pickering et al (2002); (Q) Nave et al (1991). interpolated weighted mean errors and possible errors due to scatter in the individual flux measurements.…”