On the Perils of Hyperfine Splitting: A reanalysis of Mn and Sc   Abundance Trends
  We investigate the impact of hyperfine splitting on stellar abundance analyses of Mn and Sc, and find that incorrect hfs treatment can lead to spurious abundance trends with metallicity. We estimate corrections to a recent study by Nissen et al. (2000), and find: (1) [Mn/Fe] is described by a bimodal distribution, with [Mn/Fe] ~ -0.3 for stars [Fe/H] < -0.7, and [Mn/Fe] ~ -0.05 for stars at higher metallicity, suggestive of a transition between halo/thick disk and thin disk populations. (2) The large majority of stars show nearly solar [Sc/Fe] ratios; although important deviations cannot be ruled-out. 
Jason X. Prochaska and Andrew McWilliam (Carnegie Observatories)