Iron-group Elemental Abundances in Very Low Metallicity Stars: a Fresh Look
Chris Sneden
University of Texas at Austin



What gets us into trouble is not what we don't know. It's what we know for sure that just ain't so." (Mark Twain) Starting from the mid 1990s we have believed much observational evidence pointing to non-solar abundance ratios of iron-group elements in very metal-poor halo stars. There are deep declines in [Cr/Fe], [Mn/Fe], and [Cu/Fe], and large increases in [Co/Fe]. In this talk I will suggest that such trends either do not exist or at best are much more mild than previously supposed. High resolution spectra of a small set of stars with metallicities [Fe/H] ~ -3 have been gathered with HST/STIS and ground-based facilities and have been analyzed with fresh laboratory transition data to conclude that: (a) the most reliable Fe-group abundances depend on study of ionized-species spectra; (b) abundances from neutral-species "popular" resonance lines need large NLTE corrections; and (c) significant correlated variations in [Sc,Ti,V/Fe] from star to star exist not only in our data set but in previous investigations - just not much noticed. I will discuss steps in broadening our work to a large survey now underway.