Comment on: “Hyperfine structure measurements of Co I and Co II with Fourier transform spectroscopy” by Fu et al. [JQSRT 2021, 107590

Abstract

This comment points out errors in the analysis of 61 magnetic hyperfine structure (A) constants of Co II energy levels by Fu et al. [JQSRT 2021, 107590]. The paper was published without full awareness of the extensive literature already available for Co II hyperfine A constants at the time; 57 of 58 A constants that were claimed to have been measured for the first time had already been measured by the prior work of Ding and Pickering [ApJS 2020, 251:24], who had published A constants for 292 levels of Co II. The A constant of 3d64s2 a5D4 has been determined by Fu et al. [JQSRT 2021, 107590] for the first time to be 12.0±1.8 mK (1 mK = 0.001 cm−1), which was found to agree with line profiles observed by Ding and Pickering [ApJS 2020, 251:24]. Discrepancies in 17 A constants of Fu et al. [JQSRT 2021, 107590] were found, which are likely due to the analysis of weak, experimentally unclassified transitions with Ritz wavenumbers 25453.966 cm−1 and 25149.948 cm−1 by Fu et al. [JQSRT 2021, 107590] for the A constants of the energy levels 3d7(2G)4s a3G5 and 3d7(2P)4s c3P2 respectively. Fewer transitions and poorer quality spectra analysed by Fu et al. [JQSRT 2021, 107590] are also concluded to have contributed to disagreements in the 17 A constants.