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 A), Cr ii (2066, 2062 and 2056 A) and Ni ii (1751, 1741, 1709 and 1703 A). Apart from the last line, which is very weak, the uncertainty of these measurements is 0.002 cm−1 (0.08 ma) for the lines around 2000 A and 0.004 cm−1 (0.12 ma) for the lines around 1700 A.