scholarly journals Trans-iron Ge, As, Se, and heavier elements in the dwarf metal-poor stars HD 19445, HD 84937, HD 94028, HD 140283, and HD 160617

2020 ◽  
Vol 638 ◽  
pp. A64 ◽  
Author(s):  
R. C. Peterson ◽  
B. Barbuy ◽  
M. Spite
Keyword(s):  
Abundance Ratio ◽  
Uv Spectra ◽  
Element Abundance ◽  
Elemental Abundances ◽  
Halo Stars ◽  
Abundance Patterns ◽  
Model Predictions ◽  
Line Selection ◽  
Imaging Spectrograph ◽  
Good Agreement

Context. The spectra of unevolved metal-poor halo stars uniquely reflect the elemental abundances incorporated during the earliest Galactic epoch. Their heavy-element content is well understood as the products of neutron capture on iron-peak elements. However, for the lightest trans-iron elements with atomic number 30 <  Z <  52, they show striking abundance patterns that defy model predictions. Understanding their sources may illuminate the diverse halo, thick disk, or extragalactic origins of metal-poor stars. Aims. The primary goal is the derivation of halo dwarf abundances and their uncertainties for six trans-iron elements from UV spectra, plus optical abundances for four additional trans-Fe elements and two well-understood heavier elements. Methods. For five metal-poor dwarfs, we analyzed high-resolution UV spectra from the Hubble Space Telescope Imaging Spectrograph, supplemented by archival optical echelle spectra. Two independent analyses adopted different programs, models, and line lists, clarifying systematic errors. Results. The results from the separate UV analyses are in good agreement. The largest source of discrepancy is the placement of the UV continuum. Once rectified, the separate results agree to 0.2 dex for moderately unblended, moderately strong lines. Similar agreement is found with previous works, except where new data and line selection become important, notably our exclusion of trans-Fe lines blended by newly identifed Fe I lines. Conclusions. Improved line lists lead to low As/Ge ratios that no longer require an early arsenic enhancement. All five stars exhibit a high Mo/Ge abundance ratio, independent of Mo/Fe. The trans-Fe elements show an odd-even effect: an odd-Z element abundance is depressed relative to those of adjacent even-Z elements. Its suggested metallicity dependence is supported by previous studies of Sr-Y-Zr. Some theoretical yields show a metallicity-dependent odd-even effect, but none have predicted a constant Mo/Ge abundance ratio. Our work thus highlights the complexity of predicting the production of light trans-Fe elements in metal-poor stars.

Element Abundance Patterns of Metal-Poor Halo Stars

2001 ◽  
pp. 193-193
Author(s):  
D. Argast ◽  
M. Samland ◽  
O. E. Gerhard ◽  
F.-K. Thielemann
Keyword(s):  
Element Abundance ◽  
Halo Stars ◽  
Abundance Patterns

scholarly journals Detailed elemental abundances of binary stars: Searching for signatures of planet formation and atomic diffusion

2021 ◽  
Author(s):  
Fan Liu ◽  
Bertram Bitsch ◽  
Martin Asplund ◽  
Bei-Bei Liu ◽  
Michael T Murphy ◽  
...  
Keyword(s):  
Binary Stars ◽  
Binary Systems ◽  
Planet Formation ◽  
Binary Star ◽  
The Other ◽  
Atomic Diffusion ◽  
Element Abundance ◽  
Condensation Temperature ◽  
Elemental Abundances ◽  
Abundance Patterns

Abstract Binary star systems are assumed to be co-natal and coeval, thus to have identical chemical composition. In this work we aim to test the hypothesis that there is a connection between observed element abundance patterns and the formation of planets using binary stars. Moreover, we also want to test how atomic diffusion might influence the observed abundance patterns. We conduct a strictly line-by-line differential chemical abundance analysis of 7 binary systems. Stellar atmospheric parameters and elemental abundances are obtained with extremely high precision (&lt; 3.5%) using the high quality spectra from VLT/UVES and Keck/HIRES. We find that 4 of 7 binary systems show subtle abundance differences (0.01 - 0.03 dex) without clear correlations with the condensation temperature, including two planet-hosting pairs. The other 3 binary systems exhibit similar degree of abundance differences correlating with the condensation temperature. We do not find any clear relation between the abundance differences and the occurrence of known planets in our systems. Instead, the overall abundance offsets observed in the binary systems (4 of 7) could be due to the effects of atomic diffusion. Although giant planet formation does not necessarily imprint chemical signatures onto the host star, the differences in the observed abundance trends with condensation temperature, on the other hand, are likely associated with diverse histories of planet formation (e.g., formation location). Furthermore, we find a weak correlation between abundance differences and binary separation, which may provide a new constraint on the formation of binary systems.

scholarly journals Searching for extremely alpha-poor stars in the Galactic Halo

2013 ◽  
Vol 9 (S298) ◽  
pp. 449-449
Author(s):  
Qianfan Xing ◽  
Gang Zhao
Keyword(s):  
Galactic Halo ◽  
Element Abundance ◽  
Chemical Abundance ◽  
Stellar Spectra ◽  
Large Sample ◽  
Pilot Survey ◽  
Chemical Enrichment ◽  
Halo Stars ◽  
Abundance Patterns ◽  
Abundance Trends

AbstractA few alpha-poor stars that show severe departures (over 0.4 dex deficiency in alpha-element abundance) from the general enhanced alpha-element chemical abundance trends of the halo have been discovered in recent years, such as BD +80°245, G4-36 and CS 22966-043. These ratios suggest a different chemical enrichment history for these stars than for the majority of the halo. Similarly low-alpha abundance patterns are also seen in the Sagittarius dSph galaxy. We present a method for searching of extremely alpha-poor stars from low-resolution stellar spectra of LAMOST pilot survey and attempt to create a large sample of these particular Galactic halo stars.

scholarly journals Condensation Chemistry of Circumstellar Grains

1999 ◽  
Vol 191 ◽  
pp. 279-290 ◽  
Author(s):  
Katharina Lodders ◽  
Bruce Fegley
Keyword(s):  
Trace Element ◽  
Total Pressure ◽  
Element Abundance ◽  
Elemental Abundances ◽  
Trace Element Chemistry ◽  
Abundance Patterns ◽  
Element Chemistry ◽  
Circumstellar Shells ◽  
Thermochemical Equilibrium ◽  
Equilibrium Calculations

Thermochemical equilibrium calculations are successful in predicting the mineralogy as well as the major and trace element chemistry of circumstellar grains found in meteorites. The calculations also explain observations of dust close to AGB stars (within 1–3 stellar radii). The trace element chemistry in circumstellar graphite, SiC, and other refractory carbide grains agrees with equilibrium condensation calculations for circumstellar shells of carbon stars. Observed trace element abundance patterns in N stars are complementary to those found in SiC grains indicating fractional condensation in circumstellar shells. Condensation temperatures depend upon total pressure, C/O ratio, nitrogen abundances, and overall metallicity. Therefore for condensation temperatures to be meaningful, the total pressure and elemental abundances (i.e., C/O ratio, metallicity) must be specified.

Distribution of R- and S-Process Elements in the Galactic Halo

1988 ◽  
Vol 132 ◽  
pp. 501-506
Author(s):  
C. Sneden ◽  
C. A. Pilachowski ◽  
K. K. Gilroy ◽  
J. J. Cowan
Keyword(s):  
Heavy Element ◽  
Galactic Halo ◽  
Low Noise ◽  
Heavy Elements ◽  
Process Synthesis ◽  
Element Abundances ◽  
Halo Stars ◽  
Abundance Patterns ◽  
R Process ◽  
Process Elements

Current observational results for the abundances of the very heavy elements (Z&gt;30) in Population II halo stars are reviewed. New high resolution, low noise spectra of many of these extremely metal-poor stars reveal general consistency in their overall abundance patterns. Below Galactic metallicities of [Fe/H] Ã −2, all of the very heavy elements were manufactured almost exclusively in r-process synthesis events. However, there is considerable star-to-star scatter in the overall level of very heavy element abundances, indicating the influence of local supernovas on element production in the very early, unmixed Galactic halo. The s-process appears to contribute substantially to stellar abundances only in stars more metal-rich than [Fe/H] Ã −2.

scholarly journals Light element abundance inhomogeneities in globular clusters: probing star formation and evolution in the early Milky Way

1994 ◽  
Vol 72 (11-12) ◽  
pp. 772-781 ◽  
Author(s):  
Michael M. Briley ◽  
Roger A. Bell ◽  
James E. Hesser ◽  
Graeme H. Smith
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Main Sequence ◽  
Light Element ◽  
Star Formation History ◽  
Element Abundance ◽  
Chemical Compositions ◽  
Original Material ◽  
Abundance Patterns ◽  
Red Giant

Abundance patterns of the elements C, N, and O are sensitive probes of stellar nucleosynthesis processes and, in addition, O abundances are an important input for stellar age determinations. Understanding the nature of the observed distribution of these elements is key to constraining protogalactic star formation history. Patterns deduced from low-resolution spectroscopy of the CN, CH, NH, and CO molecules for low-mass stars in their core-hydrogen or first shell-hydrogen burning phases in the oldest ensembles known, the Galactic globular star clusters, are reviewed. New results for faint stars in NGC 104 (47 Tuc, C0021-723) reveal that the bimodal, anticorrelated pattern of CN and CH strengths found among luminous evolved stars is also present in stars nearing the end of their main-sequence lifetimes. In the absence of known mechanisms to mix newly synthesized elements from the interior to the observable surface layers of such unevolved stars, those particular inhomogeneities imply that the original material from which the stars formed some 15 billion years ago was chemically inhomogeneous in the C and N elements. However, in other clusters, observations of abundance ratios and C isotope ratios suggest that alterations to surface chemical compositions are produced as stars evolve from the main sequence through the red giant branch. Thus, the current observed distributions of C, N, and O among the brightest stars (those also observed most often) may not reflect the true distribution from which the protocluster cloud formed. The picture that is emerging of the C, N, and O abundance patterns within globular clusters may be one which requires a complicated combination of stellar evolutionary and primordial effects for its explanation.

Rigid-Plastic Impact of Single Angular Particles

2021 ◽  
Author(s):  
Sandeep Dhar
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Element Model ◽  
Orientation Dependence ◽  
Particle Orientation ◽  
Rigid Plastic ◽  
Plastic Model ◽  
Model Predictions ◽  
Good Agreement ◽  
Angular Particles

The trajectory of an angular particle as it cuts a ductile target is, in general, complicated because of its dependence not only on particle shape, but also on particle orientation at the initial instant of impact. This orientation dependence has also made experimental measurement of impact parameters of single angular particles very difficult, resulting in a relatively small amount of available experimental data in the literature. The current work is focused on obtaining measurements of particle kinematics for comparison to rigid plastic model developed by Papini and Spelt. Fundamental mechanisms of material removal are identified, and measurements of rebound parameters and corresponding crater dimensions of single hardened steel particles launched against flat aluminium alloy targets are presented. Also a 2-D finite element model is developed and a dynamic analysis is performed to predict the erosion mechanism. Overall, a good agreement was found among the experimental results, rigid-plastic model predictions and finite element model predictions.

Viscosity Models Based on Network Theory for Polymer Melts

2010 ◽  
Vol 129-131 ◽  
pp. 1244-1247
Author(s):  
Hai Hang Xu ◽  
Lei Zhong
Keyword(s):  
Experimental Data ◽  
Kinetic Equation ◽  
Constitutive Equation ◽  
Polymer Composites ◽  
Network Theory ◽  
Polymer Melts ◽  
Structure Parameter ◽  
Viscosity Models ◽  
Model Predictions ◽  
Good Agreement

New shear and extensional viscosity models based on Fredrickson kinetic equation coupled with Dewitt constitutive equation were established to predict viscosities of polymer melts. The experimental data of 125°C LDPE and LDPE filled with 35% glass beads reported from references were compared with the model predictions. The predictions showed good agreement with the measurements. The models are simple and easy to use. Because they contain no structure parameter, they are capable to describe the viscosities of pure polymer and polymer composites.

Modeling the Effect of Water Activity, pH, and Temperature on the Probability of Enterotoxin A Production by Staphylococcus aureus

2016 ◽  
Vol 79 (1) ◽  
pp. 148-152 ◽  
Author(s):  
TIAN DING ◽  
YAN-YAN YU ◽  
CHENG-AN HWANG ◽  
QING-LI DONG ◽  
SHI-GUO CHEN ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Water Activity ◽  
Storage Temperature ◽  
Probability Model ◽  
Toxin Production ◽  
Factors Affecting ◽  
Model Predictions ◽  
And Storage ◽  
Storage Temperatures ◽  
Good Agreement

ABSTRACT The objectives of this study were to develop a probability model of Staphylococcus aureus enterotoxin A (SEA) production as affected by water activity (aw), pH, and temperature in broth and assess its applicability for milk. The probability of SEA production was assessed in tryptic soy broth using 24 combinations of aw (0.86 to 0.99), pH (5.0 to 7.0), and storage temperature (10 to 30°C). The observed probabilities were fitted with a logistic regression to develop a probability model. The model had a concordant value of 97.5% and concordant index of 0.98, indicating that the model satisfactorily describes the probability of SEA production. The model showed that aw, pH, and temperature were significant factors affecting the probability of toxin production. The model predictions were in good agreement with the observed values obtained from milk. The model may help manufacturers in selecting product pH and aw and storage temperatures to prevent SEA production.

A Study of Abrasive Jet Micro-Grooving of Quartz Crystals

2010 ◽  
Vol 443 ◽  
pp. 645-651 ◽  
Author(s):  
Alireza Moridi ◽  
Jun Wang ◽  
Yasser M. Ali ◽  
Philip Mathew ◽  
Xiao Ping Li
Keyword(s):  
Predictive Models ◽  
Deep Understanding ◽  
Machining Process ◽  
Micro Machining ◽  
Machining Performance ◽  
Quartz Crystals ◽  
Abrasive Jet Machining ◽  
Model Predictions ◽  
Micro Grooving ◽  
Good Agreement

Owing to its various distinct advantages over the other machining technologies, abrasive jet machining has become a promising machining technology for brittle and hard-to-machine materials. An experimental study is presented on the micro-grooving of quartz crystals using an abrasive airjet. The effect of the various process parameters on the major machining performance measures are analysed to provide a deep understanding of this micro-machining process. Predictive models are then developed for quantitatively estimating the machining performance. The models are finally verified by an experiment. It shows that the model predictions are in good agreement with the experimental results under the corresponding conditions.

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