Detailed Iron-peak Element Abundances in Three Very Metal-poor Stars*

Abstract

We have obtained new detailed abundances of the Fe-group elements Sc through Zn (Z = 21−30) in three very metal-poor ([Fe/H] ≈ −3) stars: BD+03 o 740, BD−13 o 3442, and CD−33 o 1173. High-resolution ultraviolet HST /STIS spectra in the wavelength range 2300−3050Å were gathered, and complemented by an assortment of optical echelle spectra. The analysis featured recent laboratory atomic data for number of neutral and ionized species for all Fe-group elements except Cu and Zn. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys indicates that they are positively correlated in stars with [Fe/H] < −2. The abundances of these elements in BD+03 o 740, BD−13 o 3442, CD−33 o 1173, and HD 84937 (studied in a previous paper of this series) are in accord with these trends and lie at the high end of the correlations. Six elements have detectable neutral and ionized features, and generally their abundances are in reasonable agreement. For Cr we find only minimal abundance disagreement between the neutral (mean of [Cr i/Fe] = +0.01) and ionized species (mean of [Cr ii/Fe] = +0.08), unlike most studies in the past. The prominent exception is Co, for which the neutral species indicates a significant overabundance (mean of [Co i/H] = −2.53), while no such enhancement is seen for the ionized species (mean of [Co ii/H] = −2.93). These new stellar abundances, especially the correlations among Sc, Ti, and V, suggest that models of element production in early high-mass metal-poor stars should be revisited. *

Evidence of Extended Emission in GRB 181123B and Other High-redshift Short GRBs

“…This is also supported by the detection of candidate kilonovae in some nearby sGRBs (e.g., Tanvir et al 2013;Ascenzi et al 2019;Troja et al 2019;Jin et al 2020). However, the cosmic origin of r-process elements is still far from being settled (Cowan et al 2020). Many open questions remain, among them is whether NS mergers can account for the r-process enhancement of metal-poor stars and dwarf galaxies (Beniamini et al 2016a(Beniamini et al , 2016bRoederer et al 2016;Frebel 2018;Skúladóttir et al 2018).…”

A New Set of Chisels for Galactic Archeology: Sc, V, and Zn as Taggers of Accreted Globular Clusters*

“…Unlike Zn, whose nucleosynthesis in stars is pretty well understood (see previous paragraphs), the detailed nucleosynthetic paths leading to the stellar production of Sc and V still deserve investigation (see Cowan et al 2020;Kobayashi et al 2020 for recent reappraisals from the observational and theoretical point of view, respectively). Notably, different initial conditions of exploding white dwarfs leading to type Ia supernovae may result in very different V yields (e.g., Shen et al 2018;Leung & Nomoto 2020) with sizable consequences on the predictions of chemical evolution models (Palla 2021) that have yet to be fully explored.…”

The Origin of Elements from Carbon to Uranium

“…Observationally, NLTE effects of iron-peak elements other than iron have not been well studied yet, except for a few cases (e.g., Bergemann & Gehren 2008;Bergemann et al 2010;Bergemann & Cescutti 2010). However, Sneden et al (2016) and Cowan et al (2020) obtained consistent abundances between neutral and ionized lines using updated atomic data, except for Cr and Co, which implies that the NLTE effects may not be so large. Given these previous studies, it is a matter of urgency to check the NLTE effects for iron-peak elements with updated atomic data.…”