scholarly journals Abundance Patterns Among Very Metal-Poor Stars in the Halo of the Galaxy: A Statistical Approach

2009 ◽  
Vol 5 (S262) ◽  
pp. 412-413
Author(s):  
Vinicius M. Placco ◽  
Silvia Rossi ◽  
Timothy C. Beers ◽  
Sara Lucatello
Keyword(s):  
Neutron Capture ◽  
Statistical Approach ◽  
Chemical Elements ◽  
Comprehensive Analysis ◽  
Elemental Abundances ◽  
Abundance Patterns ◽  
The Galaxy ◽  
R Process ◽  
Early Galaxy ◽  
Natural Groups

AbstractThe main goal of this work is to explore the abundance patterns of the very metal-poor stars ([Fe/H]<−2.0) observed by the HERES (Hamburg ESO R-process Enhanced Star - Christlieb et al. 2004) survey. This type of study allows the analysis of the correlations among chemical elements, and place some constraints on the operation of the neutron-capture (r and s) processes in the early Galaxy. This approach makes use of statistical tools, such as agglomerative nesting, which can identify the formation of natural groups based on relations among elemental abundances (e.g. [C/Fe], [Sr/Fe], [Ba/Fe], and [Eu/Fe]), and can also be used in a series of “large-sample like” studies.This study provides a comprehensive analysis of a sample of 326 metal-poor stars, and introduces two new subclasses (r-0 and s-I) for metal-poor stars with determined abundances of neutron-capture elements, aiming to standardize the nomenclature for those objects and, by reproducing previous results, confirms the validity of the statistical method used.

scholarly journals Silver Stars

2009 ◽  
Vol 5 (S265) ◽  
pp. 67-68
Author(s):  
Camilla Juul Hansen ◽  
Francesca Primas
Keyword(s):  
Neutron Capture ◽  
Heavy Elements ◽  
Capture Process ◽  
Elemental Abundances ◽  
The Galaxy ◽  
Formation And Evolution ◽  
R Process ◽  
Process Elements ◽  
Heaviest Elements ◽  
Process Element

AbstractThe rapid neutron-capture process (r-process), which produces some of the heaviest elements, is not well understood. Obtaining accurate abundances of these heavy elements (Z > 38) is important, both in the context of the chemical evolution of the Galaxy and for understanding the site(s) and process(es) of formation of those elements. We have determined elemental abundances for several r-process elements, notably silver, from high resolution VLT/UVES spectra. Silver was chosen because it is predominantly a light r-process element (38 < Z < 50), and little is known about its formation and evolution in the Galaxy. Here, we present our preliminary results.

60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae

Science ◽  
2021 ◽  
Vol 372 (6543) ◽  
pp. 742-745
Author(s):  
A. Wallner ◽  
M. B. Froehlich ◽  
M. A. C. Hotchkis ◽  
N. Kinoshita ◽  
M. Paul ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Neutron Stars ◽  
Neutron Capture ◽  
Half Life ◽  
Massive Stars ◽  
Chemical Elements ◽  
Capture Process ◽  
Isotopic Signatures ◽  
Supernova Explosions ◽  
R Process

Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust—iron-60 (60Fe) (half-life, 2.6 million years), which is predominantly produced in massive stars and ejected in supernova explosions, and plutonium-244 (244Pu) (half-life, 80.6 million years), which is produced solely in r-process events. We detect two distinct influxes of 60Fe to Earth in the last 10 million years and accompanying lower quantities of 244Pu. The 244Pu/60Fe influx ratios are similar for both events. The 244Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, which implies some contribution from other sources.

scholarly journals Features of Chemical-Element Abundances in Open Star Clusters of the Galaxy

2016 ◽  
Vol 25 (1) ◽  
pp. 1-9
Author(s):  
V. A. Marsakov ◽  
V. V. Koval’ ◽  
M. L. Gozha ◽  
L. V. Shpigel’
Keyword(s):  
Neutron Capture ◽  
Chemical Elements ◽  
Star Clusters ◽  
Slow Neutron ◽  
Open Star Clusters ◽  
Element Abundances ◽  
Open Star ◽  
The Galaxy ◽  
Relative Abundances ◽  
High Metallicity

AbstractOn the basis of the authors’ compiled catalog containing spectroscopic abundances of 14 chemical elements for 90 open star clusters of the Galaxy, we show that in the young clusters not only barium but also three other studied elements of slow neutron-capture, Y, La, and Ce, reveal higher relative abundances than those in the field stars, with differences beyond the error limits. We also find that, at high metallicity ([Fe/H]> −0.1), the relative abundances of the

scholarly journals Nitrogen evolution in the halo, thick disc, thin disc, and bulge of the Galaxy

2021 ◽  
Vol 508 (1) ◽  
pp. 719-727
Author(s):  
V Grisoni ◽  
F Matteucci ◽  
D Romano
Keyword(s):  
Galactic Halo ◽  
Massive Stars ◽  
Chemical Elements ◽  
Distribution Functions ◽  
Abundance Pattern ◽  
Origin And Evolution ◽  
Thick Disc ◽  
Thin Disc ◽  
Abundance Patterns ◽  
The Galaxy

ABSTRACT We study the evolution of nitrogen (N) in the Galactic halo, thick disc, thin disc, and bulge by comparing detailed chemical evolution models with recent observations. The models used in this work have already been constrained to explain the abundance patterns of α-elements and the metallicity distribution functions of halo, disc, and bulge stars; here, we adopt them to investigate the origin and evolution of N in the different Galactic components. First, we consider different sets of yields and study the importance of the various channels proposed for N production. Secondly, we apply the reference models to study the evolution of both the Galactic discs and bulge. We conclude that: i) primary N produced by rotating massive stars is required to reproduce the plateau in log(N/O) and [N/Fe] ratios at low metallicity, as well as the secondary and primary production from low- and intermediate-mass stars to reproduce the data of the thin disc; ii) the parallel model can provide a good explanation of the evolution of N abundance in the thick and thin discs, and we confirm that the thick disc has evolved much faster than the thin disc, in agreement with the results from the abundance patterns of other chemical elements; and iii) finally, we present new model predictions for N evolution in the Galactic bulge, and we show that the observations in bulge stars can be explained if massive stars rotate fast during the earliest phases of Galactic evolution, in agreement with findings from the abundance pattern of carbon.

scholarly journals Abundance patterns of the light neutron-capture elements in very and extremely metal-poor stars

2018 ◽  
Vol 611 ◽  
pp. A30 ◽  
Author(s):  
F. Spite ◽  
M. Spite ◽  
B. Barbuy ◽  
P. Bonifacio ◽  
E. Caffau ◽  
...  
Keyword(s):  
Thermodynamic Equilibrium ◽  
Neutron Capture ◽  
Local Thermodynamic Equilibrium ◽  
Abundance Patterns ◽  
Element Pattern ◽  
The Mean ◽  
R Process ◽  
Peak Abundance ◽  
Second Peak

Aims. The abundance patterns of the neutron-capture elements in metal-poor stars provide a unique record of the nucleosynthesis products of the earlier massive primitive objects. Methods. We measured new abundances of so-called light neutron-capture of first peak elements using local thermodynamic equilibrium (LTE) 1D analysis; this analysis resulted in a sample of 11 very metal-poor stars, from [Fe/H] = –2.5 to [Fe/H] = –3.4, and one carbon-rich star, CS 22949-037 with [Fe/H] = –4.0. The abundances were compared to those observed in two classical metal-poor stars: the typical r-rich star CS 31082-001 ([Eu/Fe] > +1.0) and the r-poor star HD 122563 ([Eu/Fe] < 0.0), which are known to present a strong enrichment of the first peak neutron-capture elements relative to the second peak. Results. Within the first peak, the abundances are well correlated in analogy to the well-known correlation inside the abundances of the second-peak elements. In contrast, there is no correlation between any first peak element with any second peak element. We show that the scatter of the ratio of the first peak abundance over second peak abundance increases when the mean abundance of the second peak elements decreases from r-rich to r-poor stars. We found two new r-poor stars that are very similar to HD 122563. A third r-poor star, CS 22897-008, is even more extreme; this star shows the most extreme example of first peak elements enrichment to date. On the contrary, another r-poor star (BD–18 5550) has a pattern of first peak elements that is similar to the typical r-rich stars CS 31082-001, however this star has some Mo enrichment. Conclusions. The distribution of the neutron-capture elements in our very metal-poor stars can be understood as the combination of at least two mechanisms: one that enriches the forming stars cloud homogeneously through the main r-process and leads to an element pattern similar to the r-rich stars, such as CS 31082-001; and another that forms mainly lighter, first peak elements.

scholarly journals TYC5594-576-1: R-PROCESS ENRICHMENT METAL-POOR STAR

2021 ◽  
Vol 34 ◽  
pp. 48-52
Author(s):  
T.V. Mishenina ◽  
I.A. Usenko ◽  
A.Yu. Kniazev ◽  
V. V. Kovtyukh
Keyword(s):  
Synthetic Spectrum ◽  
Carbon Abundance ◽  
The Galaxy ◽  
The Status ◽  
Molecular Synthesis ◽  
R Process ◽  
Process Elements ◽  
Early Galaxy ◽  
First Time ◽  
Poor Population

Atmospheric parameters and elemental abundances of metal-poor Population II star  TYC5594-576-1 ([Fe/H] = –2.8) have been studied, including the elements of neutron (n-) capture processes, as an important part of the enrichment sources of early Galaxy. Na, Mg, Al, Co, Sr, Y, Zr, Mo, Ba, La, Ce, Pr, Sm, Eu, Gd, Dy, Os, and Th abundances were determined using the synthetic spectrum method, taken into account the hyperfine structure (HFS) for the Ba II, La II and Eu II lines. The abundances of Si, Ca, Sc, N were determined based on the equivalent widths of their lines. The carbon abundance was obtained by the molecular synthesis fitting for the CH region of 4300-4330 ÅÅ. For the abundances determinations of C, Na, Mg, Al, Ba, and Th the NLTE corrections have been applied.We have determined the abundances of several n- capture elements for the first time and found that the behaviour of these elements abundances shows a significant trend with increasing atomic number. The elements ratios of [Eu/Fe] = 1.85, [Ba/Eu] = –1.24, [Sr/Ba] = –1.04 confirm the status of TYC5594-576-1 as a r-process enrichment star, with lower strontium [Sr/Fe] = –0.33 and higher thorium [Th/Fe] = 1.28 abundances. The obtained europium and thorium excesses testifies to the early enrichment of the Galaxy by the r-process elements as a result of the merger of neutron stars or black holes. The carbon abundance confirms the effect of canonical additional mixing in this star.

scholarly journals Heavy Element Nucleosynthesis

2018 ◽  
Vol 184 ◽  
pp. 01007
Author(s):  
Mounib F. El Eid
Keyword(s):  
Chemical Evolution ◽  
Neutron Capture ◽  
Heavy Element ◽  
Slow Neutron ◽  
Heavy Elements ◽  
Galactic Chemical Evolution ◽  
Physical Processes ◽  
The Galaxy ◽  
R Process

This contribution deals with the important subject of the nucleosynthesis of heavy elements in the Galaxy. After an overview of several observational features, the physical processes responsible mainly for the formation of heavy elements will be described and linked to possible stellar sites and to galactic chemical evolution. In particular, we focus on the neutron-capture processes, namely the s-process (slow neutron capture) and the r-process (rapid neutron capture) and discuss some problems in connection with their sites and their outcome. The aim is to give a brief overview on the exciting subject of the heavy element nucleosynthesis in the Galaxy, emphasizing its importance to trace the galactic chemical evolution and illustrating the challenge of this subject.

scholarly journals Mono-enriched stars and Galactic chemical evolution

2020 ◽  
Vol 643 ◽  
pp. A49
Author(s):  
C. J. Hansen ◽  
A. Koch ◽  
L. Mashonkina ◽  
M. Magg ◽  
M. Bergemann ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Second Generation ◽  
Asymptotic Giant Branch ◽  
Three Dimensional Model ◽  
First Stars ◽  
Abundance Pattern ◽  
Abundance Patterns ◽  
The Galaxy ◽  
Bona Fide ◽  
R Process

A long sought after goal using chemical abundance patterns derived from metal-poor stars is to understand the chemical evolution of the Galaxy and to pin down the nature of the first stars (Pop III). Metal-poor, old, unevolved stars are excellent tracers as they preserve the abundance pattern of the gas from which they were born, and hence they are frequently targeted in chemical tagging studies. Here, we use a sample of 14 metal-poor stars observed with the high-resolution spectrograph called the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) to derive abundances of 32 elements (34 including upper limits). We present well-sampled abundance patterns for all stars obtained using local thermodynamic equilibrium (LTE) radiative transfer codes and one-dimensional (1D) hydrostatic model atmospheres. However, it is currently well-known that the assumptions of 1D and LTE may hide several issues, thereby introducing biases in our interpretation as to the nature of the first stars and the chemical evolution of the Galaxy. Hence, we use non-LTE (NLTE) and correct the abundances using three-dimensional model atmospheres to present a physically more reliable pattern. In order to infer the nature of the first stars, we compare unevolved, cool stars, which have been enriched by a single event (“mono-enriched”), with a set of yield predictions to pin down the mass and energy of the Pop III progenitor. To date, only few bona fide second generation stars that are mono-enriched are known. A simple χ2-fit may bias our inferred mass and energy just as much as the simple 1D LTE abundance pattern, and we therefore carried out our study with an improved fitting technique considering dilution and mixing. Our sample presents Carbon Enhanced Metal-Poor (CEMP) stars, some of which are promising bona fide second generation (mono-enriched) stars. The unevolved, dwarf BD+09_2190 shows a mono-enriched signature which, combined with kinematical data, indicates that it moves in the outer halo and likely has been accreted onto the Milky Way early on. The Pop III progenitor was likely of 25.5 M⊙ and 0.6 foe (0.6 1051 erg) in LTE and 19.2 M⊙ and 1.5 foe in NLTE, respectively. Finally, we explore the predominant donor and formation site of the rapid and slow neutron-capture elements. In BD-10_3742, we find an almost clean r-process trace, as is represented in the star HD20, which is a “metal-poor Sun benchmark” for the r-process, while TYC5481-00786-1 is a promising CEMP-r/-s candidate that may be enriched by an asymptotic giant branch star of an intermediate mass and metallicity.

scholarly journals Enrichment of Thorium (Th) and Lead (Pb) in the early Galaxy

2009 ◽  
Vol 5 (S265) ◽  
pp. 61-62
Author(s):  
Wako Aoki ◽  
Satoshi Honda
Keyword(s):  
Neutron Capture ◽  
High Sensitivity ◽  
Process Models ◽  
Heavy Elements ◽  
Logarithmic Scale ◽  
Giant Stars ◽  
Large Dispersion ◽  
Current Sample ◽  
R Process ◽  
Early Galaxy

AbstractWe have been determining abundances of Th, Pb and other neutron-capture elements in metal-deficient cool giant stars to constrain the enrichment of heavy elements by the r- and s-processes. Our current sample covers the metallicity range between [Fe/H] = −2.5 and −1.0. (1) The abundance ratios of Pb/Fe and Pb/Eu of most of our stars are approximately constant, and no increase of these ratios with increasing metallicity is found. This result suggests that the Pb abundances of our sample are determined by the r-process with no or little contribution of the s-process. (2) The Th/Eu abundance ratios of our sample show no significant scatter, and the average is lower by 0.2 dex in the logarithmic scale than the solar-system value. This result indicates that the actinides production by the r-process does not show large dispersion, even though r-process models suggest high sensitivity of the actinides production to the nucleosynthesis environment.

scholarly journals Masses and lifetimes for r-process nucleosynthesis: FRIB outlook

2018 ◽  
Vol 178 ◽  
pp. 04002 ◽  
Author(s):  
Rebecca Surman ◽  
Matthew Mumpower
Keyword(s):  
Neutron Capture ◽  
Drip Line ◽  
Michigan State University ◽  
State University ◽  
Neutron Drip Line ◽  
Rare Isotope ◽  
Abundance Patterns ◽  
Nuclear Masses ◽  
R Process ◽  
Under Construction

Nuclear masses and lifetimes are key inputs for calculations of rapid neutron capture (r-process) nucleosynthesis. Masses and half-lives for thousands of nuclei from the valley of stability to the neutron drip line are required and only a fraction have been experimentally measured. Here we examine the promise of the Facility for Rare Isotope Beams, now under construction at Michigan State University, to dramatically reduce uncertainties in r-process abundance patterns due to uncertain masses and half-lives.

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