Hyperfine structure study of atomic niobium with enhanced sensitivity of Fourier transform spectroscopy

In an experimental setup with a high-resolution Fourier transform (FT) spectrometer and a hollow-cathode discharge, bandpass interference filters are used to enhance the sensitivity. This extension leads to an improvement of the signal-to-noise ratio in the spectrum of atomic niobium by a factor of up to 10 compared to FT spectra measured previously without filters (see Kröger et al 2010 Astron. Astrophys. 516 A70). Several additional spectral lines with low intensity have been observed. Additionally, in some intense lines, blends become visible due to the better signal-to-noise ratio. The hyperfine structure of 51 lines recorded in the wavelength range from 415 to 670 nm is analysed or re-analysed and magnetic dipole hyperfine structure constants A of 8 levels of even parity and 43 levels of odd parity are determined. Improvement of sensitivity of FT spectroscopy in the visible wavelength range enabled the determination of new hyperfine structure constants A for two energy levels of even parity, which fill the last gaps for energetically low-lying levels below 14 000 cm^-1. Additionally, ten new A constants for energetically higher lying levels of odd parity as well as several improved A values have been obtained.