912 research outputs found
An Update on the 0Z Project
We give an update on our 0Z Survey to find more extremely metal poor (EMP)
stars with [Fe/H] < -3 dex through mining the database of the Hamburg/ESO
Survey. We present the most extreme such stars we have found from ~1550
moderate resolution follow up spectra. One of these, HE1424-0241, has highly
anomalous abundance ratios not seen in any previously known halo giant, with
very deficient Si, moderately deficient Ca and Ti, highly enhanced Mn and Co,
and low C, all with respect to Fe. We suggest a SNII where the nucleosynthetic
yield for explosive alpha-burning nuclei was very low compared to that for the
hydrostatic alpha-burning element Mg, which is normal in this star relative to
Fe. A second, less extreme, outlier star with high [Sc/Fe] has also been found.
We examine the extremely metal-poor tail of the HES metallicity distribution
function (MDF). We suggest on the basis of comparison of our high resolution
detailed abundance analyses with [Fe/H](HES) for stars in our sample that the
MDF inferred from follow up spectra of the HES sample of candidate EMP stars is
heavily contaminated for [Fe/H](HES) < -3 dex; many of the supposed EMP stars
below that metallicity are of substantially higher Fe-metallicity, including
most of the very C-rich stars, or are spurious objects.Comment: to appear in conference proceedings "First Stars III", ed. B. O'Shea,
A. Heger & T.Abel, 4 pages, 2 figure
High-resolution Spectroscopy of Extremely Metal-poor Stars in the Least Evolved Galaxies: Leo IV
We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H] = â3.2, adding to the rapidly growing sample of extremely metal-poor (EMP) stars being identified in Milky Way satellite galaxies. The star is enhanced in the α elements Mg, Ca, and Ti by ~0.3 dex, very similar to the typical Milky Way halo abundance pattern. All of the light and iron-peak elements follow the trends established by EMP halo stars, but the neutron-capture elements Ba and Sr are significantly underabundant. These results are quite similar to those found for stars in the ultra-faint dwarfs Ursa Major II, Coma Berenices, Boötes I, and Hercules, suggesting that the chemical evolution of the lowest-luminosity galaxies may be universal. The abundance pattern we observe is consistent with predictions for nucleosynthesis from a Population III supernova explosion. The extremely low metallicity of this star also supports the idea that a significant fraction (âł10%) of the stars in the faintest dwarfs have metallicities below [Fe/H] = â3.0
Hydrogen bonding in substituted nitroanilines : isolated nets in 1,3-diamino-4-nitrobenzene and continuously interwoven nets in 3,5-dinitroaniline
Peer reviewedPublisher PD
Effects of an in-service training program using the routines-based interview
The focus of this study is an in-service training program rooted in routines-based early intervention and designed to improve the quality of goals and objectives on individualized plans. Participants were local intervention team members and other professionals who worked closely with each team. This training program involved a small number of trainees per group, providing multiple learning experiences across time and various opportunities for self-assessment and monitoring. We investigated (a) the perceptions of the participants about the strengths and weaknesses of the training program, (b) medium-term outcomes of the training with a comparison group, (c) and variables associated with the quality of goals and objectives. This study involved training more than 200 professionals, and results support the effectiveness of the program in improving the quality of goals and objectives, showing the importance of the routines-based interview in producing that improvement.info:eu-repo/semantics/acceptedVersio
Computational fluid dynamics-based surrogate optimization of a wind turbine blade tip extension for maximising energy production
The Frequency of Carbon Stars Among Extremely Metal-Poor Stars
We demonstrate that there are systematic scale errors in the [Fe/H] values
determined by the Hamburg/ESO Survey (and by inference by the HK Survey in the
past) for certain extremely metal poor highly C-enhanced giants. The
consequences of these scale errors are that a) the fraction of carbon stars at
extremely low metallicities has been overestimated in several papers in the
recent literature b) the number of extremely metal poor stars known is somewhat
lower than has been quoted in the recent literature c) the yield for extremely
metal poor stars by the HES Survey is somewhat lower than is stated in the
recent literature. A preliminary estimate for the frequency of Carbon stars
among the giants in the HES sample with -4 < [Fe/H] < -2.0 dex is 7.4 +-2.9%;
adding an estimate for the C-enhanced giants with [C/Fe] > 1.0 dex without
detectable C2 bands raises the fraction to 14 +-4$%.
We rely on the results of an extensive set of homogeneous detailed abundance
analyses of stars expected to have [Fe/H] < -3.0 dex selected from the HES to
establish these claims. We have found that the Fe-metallicity of the cooler
(Teff < 5200K) C-stars as derived from spectra taken with HIRES at Keck are a
factor of ~10 higher than those obtained via the algorithm used by the HES
project to analyze the moderate resolution follow-up spectra, which is
identical to that used until very recently by the HK Survey. This error in
Fe-abundance estimate for C-stars arises from a lowering of the emitted flux in
the continuum bandpasses of the KP (3933 A line of CaII) and particularly the
HP2 (Hdelta) indices used to estimate [Fe/H] due to absorption from strong
molecular bands.Comment: Accepted to the ApJL after a very lengthly duel with the 3
simultaneous referee
New Extremely Metal-Poor Stars in the Galactic Halo
We present a detailed abundance analysis based on high resolution and high
signal-to-noise spectra of eight extremely metal poor (EMP) stars with [Fe/H] <
-3.5-$2429, another sample
star, has excesses of N and Sc with respect to Fe. The strong outliers in
abundance ratios among the Fe-peak elements in these C-normal stars, not found
at somewhat higher metallicities, are definitely real. They suggest that at
such low metallicities we are beginning to see the anticipated and long sought
stochastic effects of individual supernova events contributing to the Fe-peak
material within a single star. A detailed comparison of the results of the
analysis procedures adopted by our 0Z project compared to those of the First
Stars VLT Large Project finds a systematic difference for [Fe/H] of ~0.3 dex,
our values always being higher.Comment: Accepted to the Ap
Mating Ewes on Condensed Tannin-Containing Forages Increases Ewe Reproductive Rate and Reduces Lamb Mortality
Action of condensed tannin (CT) reduces forage protein degradation in the rumen and increases the absorption of amino acids from the small intestine (Barry & McNabb 1999). This paper reports the effects of grazing ewes on two CT-containing forages during mating upon ewe reproductive rate and lamb mortality
The early phases of Milky Way's chemical evolution
The earliest phases of the chemical evolution of our Galaxy are analysed in
the light of the recent VLT results (concerning abundance patterns in the most
metal-poor stars of the Galactic halo) and of stellar nucleosynthesis
calculations. It is argued that: 1) the unexpected abundance patterns observed
in Pop. II stars are not the imprints of an early generation of supermassive
Pop. III stars; 2) among the various suggestions made to exlain the observed
abundance patterns, nucleosynthesis in asymmetric supernova explosions appears
most promising. In the latter case, an indirect correlation between asymmetry
and metallicity is suggested by the data. Finally, the VLT data confirm two old
``puzzles'': the existence of primary N early in Galaxy's evolution (which
constrains the mixing of protons with He-burning products in massive stars) and
the absence of dispersion in abundance ratios, at least up to the Fe peak, in
the early Galaxy (which bears on the timescales of homogeneisation of the
interstellar medium, but also on yield variations among massive stars).Comment: 10 pages, 4 figures, Review talk in Nuclei in the Cosmos VIII (Eds.
L. Buchmann et al.) to appear in NuclPhys
Multi-Element Abundance Measurements from Medium-Resolution Spectra. IV. Alpha Element Distributions in Milky Way Dwarf Satellite Galaxies
We derive the star formation histories of eight dwarf spheroidal (dSph) Milky
Way satellite galaxies from their alpha element abundance patterns. Nearly 3000
stars from our previously published catalog (Paper II) comprise our data set.
The average [alpha/Fe] ratios for all dSphs follow roughly the same path with
increasing [Fe/H]. We do not observe the predicted knees in the [alpha/Fe] vs.
[Fe/H] diagram, corresponding to the metallicity at which Type Ia supernovae
begin to explode. Instead, we find that Type Ia supernova ejecta contribute to
the abundances of all but the most metal-poor ([Fe/H] < -2.5) stars. We have
also developed a chemical evolution model that tracks the star formation rate,
Types II and Ia supernova explosions, and supernova feedback. Without metal
enhancement in the supernova blowout, massive amounts of gas loss define the
history of all dSphs except Fornax, the most luminous in our sample. All six of
the best-fit model parameters correlate with dSph luminosity but not with
velocity dispersion, half-light radius, or Galactocentric distance.Comment: 28 pages, 14 figures; accepted for publication in ApJ; very minor
editorial corrections in v
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