Chemical Abundances

Pregalactic metal enrichment: The chemical signatures of the first stars

The emergence of the first sources of light at redshifts of z˜10-30 signaled the transition from the simple initial state of the Universe to one of increasing complexity. Recent progress in our understanding of the formation of the first stars and galaxies, starting with cosmological initial conditions, primordial gas cooling, and subsequent collapse and fragmentation are reviewed. The important open question of how the pristine gas was enriched with heavy chemical elements in the wake of the first supernovae is emphasized.

The Chemical Signature of a Relic Star Cluster in the Sextans Dwarf Spheroidal Galaxy—Implications for Near-field Cosmology

We present tentative evidence for the existence of a dissolved star cluster at [Fe/H] = -2.7 in the Sextans dwarf spheroidal galaxy. We use the technique of chemical tagging to identify stars that are highly clustered in a multi-dimensional chemical abundance space ( {C}-space). In a sample of six stars, three, possibly four, stars are identified as potential cluster stars.

The Chemical Signatures of the First Star Clusters in the Universe

The chemical abundance patterns of the oldest stars in the Galaxy are expected to contain residual signatures of the first stars in the early universe. Numerous studies attempt to explain the intrinsic abundance scatter observed in some metal-poor populations in terms of chemical inhomogeneities dispersed throughout the early Galactic medium due to discrete enrichment events. Just how the complex data and models are to be interpreted with respect to "progenitor yields" remains an open question. Here we show that stochastic chemical evolution models to date have overlooked a crucial fact.

Reconstructing Fossil Sub-structures of the Galactic Disk: Clues from Abundance Patterns of Old Open Clusters and Moving Groups

The long term goal of large-scale chemical tagging is to use stellar elemental abundances as a tracer of dispersed substructures of the Galactic disk. The identification of such lost stellar aggregates and the exploration of their chemical properties will be key in understanding the formation and evolution of the disk. Present day stellar structures such as open clusters and moving groups are the ideal testing grounds for the viability of chemical tagging, as they are believed to be the remnants of the original larger star-forming aggregates.

Chemical Homogeneity in Collinder 261 and Implications for Chemical Tagging

This paper presents abundances for 12 red giants of the old open cluster Collinder 261 based on spectra from the Very Large Telescope UVES. Abundances were derived for Na, Mg, Si, Ca, Mn, Fe, Ni, Zr, and Ba. We find that the cluster has a solar-level metallicity of [Fe/H]=-0.03 dex. However, most α- and s-process elements were found to be enhanced. The star-to-star scatter was consistent with the expected measurement uncertainty for all elements. The observed rms scatter is as follows: Na=0.07, Mg=0.05, Si=0.06, Ca=0.05, Mn=0.03, Fe=0.02, Ni=0.04, Zr=0.12, and Ba=0.03 dex.

Chemically Tagging the HR 1614 Moving Group

We present abundances for a sample of F, G, and K dwarfs of the HR 1614 moving group based on high-resolution, high signal-to-noise ratio spectra from the Anglo-Australian Telescope UCLES instrument. Our sample includes stars from Feltzing and Holmberg, as well as from Eggen. Abundances were derived for Na, Mg, Al, Si, Ca, Mn, Fe, Ni, Zr, Ba, Ce, Nd, and Eu. The α, Fe, and Fe-peak element abundances show a bimodal distribution, with four stars having solar metallicities, while the remaining 14 stars are metal-rich, [Fe/H]>=0.25 dex.

Chemical Homogeneity in the Hyades

We present an abundance analysis of the heavy elements Zr, Ba, La, Ce, and Nd for Hyades F-K dwarfs based on high-resolution, high signal-to-noise ratio spectra from Keck HIRES. The derived abundances show the stellar members to be highly uniform, although some elements show a small residual trend with temperature. The rms scatter for each element for the cluster members is as follows: Zr=0.055, Ba=0.049, Ce=0.025, La=0.025, and Nd=0.032 dex. This is consistent with the measurement errors and implies that there is little or no intrinsic scatter among the Hyades members.

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