1,354,382 research outputs found
New Results From Bright Metal-Poor Stars In The Hamburg/Eso Survey
No full textWe 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
No full textWe 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 deg(2) of the southern high Galactic latitude sky. The candidate sample consists of 20 271 stars in the magnitude range 10 less than or similar to B less than or similar to 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2mag 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.Astronom
What is it like to have dementia? - Epistemological problems and filmic approaches in the bioethical debate
No full textThe perspectives of those affected play a central role in contemporary bioethics. In the case of dementia, however, these perspectives seem to become increasingly inaccessible. In the last 15 years, there has been a surge of motion pictures that deal with the experience of dementia. This paper explores in how far film can open a new approach to the perspectives of persons affected by dementia and thus contribute to the bioethical discussion. Three filmic approaches are examined, explained on the basis of concrete examples, and discussed from an ethical point of view. The specific potential of film for the bioethical discussion of dementia is hardly exhausted and calls for systematic consideration
[2 + 2] Cycloaddition of a diphosphene to maleimide and N-methylmaleimide. X-ray structure analysis of a 4,5-diphospha-2-azabicyclo[3.2.0]hepta-1,3-dione
No full textWeber L, Frebel M, Müller A, Bögge H. [2 + 2] Cycloaddition of a diphosphene to maleimide and N-methylmaleimide. X-ray structure analysis of a 4,5-diphospha-2-azabicyclo[3.2.0]hepta-1,3-dione. Organometallics. 1991;10(4):1130-1135
[1+4]-Cycloaddition eines Diphosphens an Acrolein - Synthese und Struktur eines cyclischen Phosphoranylidenphosphans
No full textWeber L, Frebel M, Boese R. [1+ 4] Cycloaddition of a Diphosphene to Acrolein: Synthesis and Structure of a Dihydro-1,2λ5-oxaphosphole with an Exocyclic P = P Bond. Angewandte Chemie International Edition in English. 1987;26(10):1010-1011
JINAbase—A Database for Chemical Abundances of Metal-poor Stars
No full textReconstructing the chemical evolution of the Milky Way is crucial for understanding the formation of stars, planets, and galaxies throughout cosmic time. Different studies associated with element production in the early universe and how elements are incorporated into gas and stars are necessary to piece together how the elements evolved. These include establishing chemical abundance trends, as set by metal-poor stars, comparing nucleosynthesis yield predictions with stellar abundance data, and theoretical modeling of chemical evolution. To aid these studies, we have collected chemical abundance measurements and other information, such as stellar parameters, coordinates, magnitudes, and radial velocities, for extremely metal-poor stars from the literature. The database, JINAbase, contains 1659 unique stars, 60% of which have [Fe/H] ≤ −2.5. This information is stored in an SQL database, together with a user-friendly queryable web application (http://jinabase.pythonanywhere.com).
Objects with unique chemical element signatures (e.g., r-process stars, s-process and CEMP stars) are labeled or can be classified as such. We find that the various neutron-capture element signatures occur in up to 19% of metalpoor stars with [Fe/H] ≤ −2.0, and 32% when also considering carbon enhancement. The web application enables fast selection of customized comparison samples from the literature for the aforementioned studies and many more. Using multiple entries for three of the most well-studied metal-poor stars, we evaluate systematic uncertainties of chemical abundance measurements between the different studies. We provide a brief guide to the selection of chemical elements for model comparisons for non-spectroscopists who wish to learn about metal-poor stars and the
details of chemical abundance measurements. Key words: astronomical databases: miscellaneous – catalogs – nuclear reactions, nucleosynthesis, abundances – stars: abundances – stars: Population IINational Science Foundation (U.S.) (PHY 14- 30152
[1+4] Cycloaddition of a Diphosphene to α,β unsaturated Carbonyl Compounds: Synthesis of Dihydro-1,2-λ5-oxaphospholes with Exocyclic P=P-Bonds and X-ray Structure Analysis of (η5-C5Me5)(CO)2Fe-P[OCH=CH-CH2](=PAr) (Ar = 2,4,6-t-Bu3C6H2)
No full textWeber L, Frebel M, Boese R. [1+4] Cycloaddition of a Diphosphene to α,β unsaturated Carbonyl Compounds: Synthesis of Dihydro-1,2-λ5-oxaphospholes with Exocyclic P=P-Bonds and X-ray Structure Analysis of (η5-C5Me5)(CO)2Fe-P[OCH=CH-CH2](=PAr) (Ar = 2,4,6-t-Bu3C6H2). Organometallics. 1989;8(7):1718-1722
HE 1327−2326, an unevolved star with [Fe/H]<−5.0. - II. New 3D−1D corrected abundances from a Very Large Telescope UVES spectrum
No full textWe present a new abundance analysis of HE 1327-2326, which is currently the most iron-poor star, based on observational data obtained with the VLT Ultraviolet and Visual Echelle Spectrograph (UVES). We correct the one-dimensional (1D) LTE abundances for three-dimensional (3D) effects to provide an abundance pattern that supersedes previous works and should be used to observationally test current models of the chemical yields of the first-generation supernovae (SNe). Apart from confirming the 1D LTE abundances found in previous studies before accounting for 3D effects, we make use of a novel technique to apply the 3D 1D corrections for CNO which are a function of excitation potential and line strength for the molecular lines that comprise the observable CH, NH, and OH features. We find that the fit to the NH band at 33608 is greatly improved due to the application of the 3D-1D corrections. This may indicate that 3D effects are actually observable in this star. We also report the first detection of several weak Ni lines. The cosmologically important element Li is still not detected; the new Li upper limit is extremely low, A(Li) < 0: 62, and in stark contrast with results not only from the Wilkinson Microwave Anisotropy Probe (WMAP) but also from other metal-poor stars. We also discuss how the new corrected abundance pattern of HE 1327-2326 is being reproduced by individual and integrated yields of SNe.W.J. McDonald FellowshipDeutsche Forschungsgemeinschaft Ch 214/3, Re 353/44Knut and Alice Wallenberg FoundationMcDonald Observator
Reconstructing the Cosmic Evolution of the Chemical Elements
No full textThe chemical elements are created in nuclear fusion processes in the hot and dense cores of stars. The energy generated through nucleosynthesis allows stars to shine for billions of years. When these stars explode as massive supernovae, the newly made elements are expelled, chemically enriching the surrounding regions. Subsequent generations of stars are formed from gas that is slightly more element-enriched than that from which previous stars formed. This chemical evolution can be traced back to its beginning soon after the Big Bang by studying the oldest and most metal-poor stars still observable in the Milky Way today. Through chemical analysis, they provide the only available tool for gaining information about the nature of the short-lived first stars and their supernova explosions more than thirteen billion years ago. These events set in motion the transformation of the pristine universe into a rich cosmos of chemically diverse planets, stars, and galaxies
The GMT-Consortium Large Earth Finder (G-CLEF): an optical Echelle spectrograph for the Giant Magellan Telescope (GMT)
No full textThe GMT-Consortium Large Earth Finder (G-CLEF) will be a cross-dispersed, optical band echelle spectrograph to be delivered as the first light scientific instrument for the Giant Magellan Telescope (GMT) in 2022. G-CLEF is vacuum enclosed and fiber-fed to enable precision radial velocity (PRV) measurements, especially for the detection and characterization of low-mass exoplanets orbiting solar-type stars. The passband of G-CLEF is broad, extending from 3500Å to 9500Å. This passband provides good sensitivity at blue wavelengths for stellar abundance studies and deep red response for observations of high-redshift phenomena. The design of G-CLEF incorporates several novel technical innovations. We give an overview of the innovative features of the current design. G-CLEF will be the first PRV spectrograph to have a composite optical bench so as to exploit that material's extremely low coefficient of thermal expansion, high in-plane thermal conductivity and high stiffness-to-mass ratio. The spectrograph camera subsystem is divided into a red and a blue channel, split by a dichroic, so there are two independent refractive spectrograph cameras. The control system software is being developed in model-driven software context that has been adopted globally by the GMT. G-CLEF has been conceived and designed within a strict systems engineering framework. As a part of this process, we have developed a analytical toolset to assess the predicted performance of G-CLEF as it has evolved through design phases
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