New Results From Bright Metal-Poor Stars In The Hamburg/Eso Survey

We present an abundance analysis of BE 1327-2326, currently the most iron-poor star known, based on a newly acquired VLT spectrum. The ID abundance pattern is corrected for 3D effects. The 3D iron abundance is [Fe/H] = -5.9, while the CNO elements of the star are extremely overabundant [CNO[Fe] similar to 3 to 4). The cosmologically important element Li is still not detected; the new upper limit is A (Li) < 0.6. A new analysis of the medium-resolution data of the sample of bright metal-poor stars from the Hamburg/ESO Survey (HES) was carried out. We are using this sample to obtain clues to the chemical nature of the early Universe by investigating the kinematic properties of the sample. Based on estimated [Fe/H] and [C/Fe], we are also able to use the sample to test a formation mechanism for low-mass metal-poor stars.Astronom

The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars

We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the Ca II K line, B-V colors (both measured directly from the digital HES spectra), as well as J-K colors from the 2 Micron All Sky Survey. The KP index for Ca II K can be measured from the HES spectra with an accuracy of 1.0 Angstrom, and a calibration of the HES B-V colors, using CCD photometry, yields a 1-sigma uncertainty of 0.07 mag for stars in the color range 0.3 < B-V < 1.4. These accuracies make it possible to reliably reject stars with [Fe/H] > -2.0 without sacrificing completeness at the lowest metallicities. A test of the selection using 1121 stars of the HK survey of Beers, Preston, and Shectman present on HES plates suggests that the completeness at [Fe/H] < -3.5 is close to 100% and that, at the same time, the contamination of the candidate sample with false positives is low: 50% of all stars with [Fe/H] > -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected. The selection was applied to 379 HES fields, covering a nominal area of 8853 square degrees of the southern high Galactic latitude sky. The candidate sample consists of 20,271 stars in the magnitude range 10 < B < 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2 mag fainter. Taking the overlap of the sky areas covered by both surveys into account, it follows that the survey volume for metal-poor stars has been increased by the HES by about a factor of 10 with respect to the HK survey. We have already identified several very rare objects with the HES, including, e.g., the three most heavy-element deficient stars currently known.Comment: 11 pages, 10 figures, accepted for publication in A&

THE EFFECTS OF ANKLE BRACING ON SPORTS-SPECIFIC CAPABILITIES

INTRODUCTION Ankle braces are widely used in athletes. In some professional sports leagues it is mandatory to wear ankle braces in order to get insurance. Even prophylactic bracing is often used in normal sports. The efficiency of ankle joint orthoses was already demonstrated in several studies, and different types of external stabilization devices were compared. Especially the. aspects of mechanical stabilization were discussed in these studies as well as retrospective observations of the prophylactic benefit regarding the prevention of sprains by using orthoses. Neurophysiological or psychological aspects are hardly taken into consideration in the literature when evaluating different types of orthoses. In the presented study the proprioception with regard to the ankle joint and especially its influence by orthoses and the effect of ankle braces on sports- specific capabilities will be discussed. First of all the question is, whether the orthoses have an impact on the proprioception of the ankle joint at all. If there is an influence, then it is of particular importance for a comprehensive judgement to document the degree of influence by each type of orthoses for the injured and not injured ankle joint. By evaluating the results of this study a possible reduction of the proprioception caused by ankle sprains will be investigated as well. This phenomenon of a posttraumatic proprioceptive deficit was already described and controversially discussed in the literature. MATERIALS AND METHODS The influence of four stabilizing devices (aircast brace, . ligafix air-brace, malleoloc-brace, taping) on sportsspecific capabilities and propioceptivity of stable and unstable ankle joints were assessed. Therefore both ankle joints of 18 uninjured volunteers and 23 injured volunteers with an old ankle sprain were tested with two different set-ups (modified Japan-test, 5 point single leg jump test). We used a modular coordination-testsystem with 5 contact plates and a computer monitor that gives in randomised sequence the signal which circles of the 5 plates to jump on. RESULTS The time for both tests as well as reaction time and contact time for each moving direction was measured and calculated by a software program. Regarding the modified Japan-test and the 5 point single leg jump test the injured group achieved showed significant better results (p< 0.01) & (

Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor

Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. Based on the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. However, verification of the iron-deficiency and measurements of additional elements, such as the alpha-element Mg, are mandatory for demonstrating that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming the iron abundance of less than 1/4000th that of the Sun, and showing that the overall abundance pattern mirrors that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical.Comment: 16 pages, including 2 figures. Accepted for publication in Nature. It is embargoed for discussion in the press until formal publication in Natur

The R-Process Alliance: A Comprehensive Abundance Analysis of HD 222925, a Metal-Poor Star with an Extreme R-Process Enhancement of [Eu/H] = -0.14

We present a detailed abundance analysis of the bright (V = 9.02), metal-poor ([Fe/H] = -1.47 +/- 0.08) field red horizontal-branch star HD 222925, which was observed as part of an ongoing survey by the R-Process Alliance. We calculate stellar parameters and derive abundances for 46 elements based on 901 lines examined in a high-resolution optical spectrum obtained using the Magellan Inamori Kyocera Echelle spectrograph. We detect 28 elements with 38 <= Z <= 90; their abundance pattern is a close match to the Solar r-process component. The distinguishing characteristic of HD 222925 is an extreme enhancement of r-process elements ([Eu/Fe] = +1.33 +/- 0.08, [Ba/Eu] = -0.78 +/- 0.10) in a moderately metal-poor star, so the abundance of r-process elements is the highest ([Eu/H] = -0.14 +/- 0.09) in any known r-process-enhanced star. The abundance ratios among lighter (Z <= 30) elements are typical for metal-poor stars, indicating that production of these elements was dominated by normal Type II supernovae, with no discernible contributions from Type Ia supernovae or asymptotic giant branch stars. The chemical and kinematic properties of HD 222925 suggest it formed in a low-mass dwarf galaxy, which was enriched by a high-yield r-process event before being disrupted by interaction with the Milky Way.Comment: Accepted for publication in the Astrophysical Journal (17 pages, 4 figures, 3 tables

Exploring the Universe with Metal-Poor Stars

The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena. Since the most metal-poor Galactic stars (with metallicities down to [Fe/H]\sim-5.5) are relics from the high-redshift Universe, they probe the chemical and dynamical conditions of the Milky Way and the origin and evolution of the elements through nucleosynthesis. They also provide constraints on the nature of the first stars, their associated supernovae and initial mass function, and early star and galaxy formation. The Milky Way's dwarf satellites contain a large fraction (~30%) of the known most metal-poor stars that have chemical abundances that closely resemble those of equivalent halo stars. This suggests that chemical evolution may be universal, at least at early times, and that it is driven by massive, energetic SNe. Some of these surviving, ultra-faint systems may show the signature of just one such PopIII star; they may even be surviving first galaxies. Early analogs of the surviving dwarfs may thus have played an important role in the assembly of the old Galactic halo whose formation can now be studied with stellar chemistry. Following the cosmic evolution of small halos in simulations of structure formation enables tracing the cosmological origin of the most metal-poor stars in the halo and dwarf galaxies. Together with future observations and additional modeling, many of these issues, including the reionization history of the Milky Way, may be constrained this way. The chapter concludes with an outlook about upcoming observational challenges and ways forward is to use metal-poor stars to constrain theoretical studies.Comment: 34 pages, 11 figures. Book chapter to appear in "The First Galaxies - Theoretical Predictions and Observational Clues", 2012 by Springer, eds. V. Bromm, B. Mobasher, T. Wiklin

Evidence for multiple nucleosynthetic processes from carbon enhanced metal-poor stars in the Carina dwarf spheroidal galaxy

Context: Carbon Enhanced Metal-Poor (CEMP) stars ($\mathrm{[C/Fe]} > 0.7$) are known to exist in large numbers at low metallicity in the Milky Way halo and are important tracers of early Galactic chemical evolution. However, very few such stars have been identified in the classical dwarf spheroidal (dSph) galaxies, and detailed abundances, including neutron-capture element abundances, have only been reported for 12 stars. Aims: We aim to derive detailed abundances of six CEMP stars identified in the Carina dSph and compare the abundances to CEMP stars in other dSph galaxies and the Milky Way halo. This is the largest sample of CEMP stars in a dSph galaxy analysed to date. Methods: 1D LTE elemental abundances are derived via equivalent width and spectral synthesis using high-resolution spectra of the six stars obtained with the MIKE spectrograph at Las Campanas Observatory. Results: Abundances or upper limits are derived for up to 27 elements from C to Os in the six stars. The analysis reveals one of the stars to be a CEMP-no star with very low neutron-capture element abundances. In contrast, the other five stars all show enhancements in neutron-capture elements in addition to their carbon enhancement, classifying them as CEMP-$s$ and -$r/s$ stars. The six stars have similar $\alpha$ and iron-peak element abundances as other stars in Carina, except for the CEMP-no star, which shows enhancement in Na, Mg, and Si. We explore the absolute carbon abundances ($A(\rm C)$) of CEMP stars in dSph galaxies and find similar behaviour as is seen for Milky Way halo CEMP stars, but highlight that CEMP-$r/s$ stars primarily have very high $A(\rm C)$ values. We also compare the neutron-capture element abundances of the CEMP-$r/s$ stars in our sample to recent $i$-process yields, which provide a good match to the derived abundances.Comment: 14 pages, 5 figures, 9 tables, Accepted for publication in A&

The stellar content of the Hamburg/ESO survey VI. The metallicity distribution of main-sequence turnoff stars in the Galactic halo

We determine the metallicity distribution function (MDF) of the Galactic halo based on metal-poor main-sequence turnoff-stars (MSTO) which were selected from the Hamburg/ESO objective-prism survey (HES) database. Corresponding follow-up moderateresolution observations (R ~ 2000) of some 682 stars (among which 617 were accepted program stars) were carried out with the 2.3m telescope at the Siding Spring Observatory (SSO). Corrections for the survey volume covered by the sample stars were quantitatively estimated and applied to the observed MDF. The corrections are quite small, when compared with those for a previously studied sample of metal-poor giants. The corrected observational MDF of the turnoff sample was then compared with that of the giants, as well as with a number of theoretical predictions of Galactic chemical evolution, including the mass-loss modified Simple Model. Although the survey-volume corrected MDFs of the metal-poor turnoff and the halo giants notably differ in the region of [Fe/H] > -2.0, below [Fe/H] ~ -2.0, (the region we scientifically focus on most) both MDFs show a sharp drop at [Fe/H] ~ -3.6 and present rather similar distributions in the low-metallicity tail. Theoretical models can fit some parts of the observed MDF, but none is found to simultaneously reproduce the peak as well as the features in the metal-poor region with [Fe/H] between -2.0 to -3.6. Among the tested models only the GAMETE model, when normalized to the tail of the observed MDF below [Fe/H] ~ -3.0, and with Z_{cr} = 10^{-3.4}Z_{\odot}, is able to predict the sharp drop at [Fe/H] ~ -3.6.Comment: 10 pages, 11 figures, accepted for publication in A&

An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars

We present a high-resolution elemental-abundance analysis for a sample of 23 very metal-poor (VMP; [Fe/H] < -2.0) stars, 12 of which are extremely metal-poor (EMP; [Fe/H] < -3.0), and 4 of which are ultra metal-poor (UMP; [Fe/H] < -4.0). These stars were targeted to explore differences in the abundance ratios for elements that constrain the possible astrophysical sites of element production, including Li, C, N, O, the alpha-elements, the iron-peak elements, and a number of neutron-capture elements. This sample substantially increases the number of known carbon-enhanced metal-poor (CEMP) and nitrogen-enhanced metal-poor (NEMP) stars -- our program stars include eight that are considered "normal" metal-poor stars, six CEMP-no stars, five CEMP-s stars, two CEMP-r stars, and two CEMP-r/s stars. One of the CEMP-$r$ stars and one of the CEMP-r/s stars are possible NEMP stars. We detect lithium for three of the six CEMP-no stars, all of which are Li-depleted with respect to the Spite plateau. The majority of the CEMP stars have [C/N] > 0. The stars with [C/N] < 0 suggest a larger degree of mixing; the few CEMP-no stars that exhibit this signature are only found at [Fe/H] < -3.4, a metallicity below which we also find the CEMP-no stars with large enhancements in Na, Mg, and Al. We confirm the existence of two plateaus in the absolute carbon abundances of CEMP stars, as suggested by Spite et al. We also present evidence for a "floor" in the absolute Ba abundances of CEMP-no stars at A(Ba)~ -2.0.Comment: 20 pages, 16 figures, Accepted for publication in Ap