scholarly journals Chemical Evolution of Galaxies: Abundance Trends and Implications

1991 ◽  
Vol 145 ◽  
pp. 13-19
Author(s):  
James W. Truran
Keyword(s):  
Massive Stars ◽  
Current Knowledge ◽  
Spectroscopic Studies ◽  
Early History ◽  
Elemental Abundance ◽  
Type Ii ◽  
Halo Stars ◽  
Abundance Patterns ◽  
Abundance Trends ◽  
History Of

Recent spectroscopic studies of the elemental abundance patterns associated with extremely metal deficient field halo stars and globular cluster stars are briefly reviewed. These metal deficient stellar populations have been found to be characterized by abundance patterns which differ quite distinctly from those of solar system abundances, but are consistent with the view that they reflect primarily the nucleosynthesis products of the evolution of massive stars and associated Type II supernovae. Guided by our current knowledge of nucleosynthesis as a function of stellar mass occurring in stars and supernovae, we identify some interesting constraints upon theories of the formation and early history of our Galaxy.

scholarly journals Abundance Clues to Early Galactic Chemical Evolution

1988 ◽  
Vol 132 ◽  
pp. 577-583 ◽  
Author(s):  
James W. Truran
Keyword(s):  
Chemical Evolution ◽  
Globular Cluster ◽  
Current Knowledge ◽  
Spectroscopic Studies ◽  
Early History ◽  
Galactic Chemical Evolution ◽  
Abundance Patterns ◽  
History Of ◽  
Halo Population ◽  
Theoretical Considerations

High S/N spectroscopic studies of the abundance patterns characterizing extremely metal-deficient halo field stars and globular cluster stars have served to provide significant clues to and increasingly stringent boundary conditions upon the chemical evolution of the halo population of our galaxy. Guided by our current knowledge of nucleosynthesis as a function of stellar mass occurring in stars and supernovae, we identify some interesting constraints that these combined observational and theoretical considerations impose upon theories of the early history of our galaxy.

scholarly journals Abundances in Stars with Exoplanets

2004 ◽  
Vol 219 ◽  
pp. 343-354 ◽  
Author(s):  
Garik Israelian
Keyword(s):  
Current Knowledge ◽  
Chemical Elements ◽  
Planetary Systems ◽  
Spectroscopic Studies ◽  
Abundance Trends

Extensive spectroscopic studies of stars with and without planets have concluded that stars hosting planets are significantly more metal-rich than those without planets. More subtle trends of different chemical elements begin to appear as the number of detected extrasolar planetary systems continues to grow. I review our current knowledge concerning the observed abundance trends of various chemical elements in stars with exoplanets and their possible implications.

scholarly journals Supernova Yields for Chemical Evolution Modeling

2013 ◽  
Vol 9 (S298) ◽  
pp. 154-166
Author(s):  
Ken'ichi Nomoto ◽  
Tomoharu Suzuki
Keyword(s):  
Chemical Evolution ◽  
Massive Stars ◽  
Elemental Abundance ◽  
Solar Abundance ◽  
Abundance Pattern ◽  
Chemical Enrichment ◽  
Abundance Patterns ◽  
Yield Table ◽  
Supernova Explosions ◽  
Evolution Modeling

AbstractWe review the recent results of the nucleosynthesis yields of massive stars. We examine how those yields are affected by some hydrodynamical effects during the supernova explosions, namely, explosion energies from those of hypernovae to faint supernovae, mixing and fallback of processed materials, asphericity, etc. Those parameters in the supernova nucleosynthesis models are constrained from observational data of supernovae and metal-poor stars. The elemental abundance patterns observed in extremely metal-poor stars show some peculiarities relative to the solar abundance pattern, which suggests the important contributions of hypernovae and faint supernovae in the early chemical enrichment of galaxies. These constraints on supernova nucleosynthesis are taken into account in the latest yield table for chemical evolution modeling.

Chemical hormesis: its historical foundations as a biological hypothesis

2000 ◽  
Vol 19 (1) ◽  
pp. 2-31 ◽  
Author(s):  
E J Calabrese ◽  
L A Baldwin
Keyword(s):  
Risk Assessment ◽  
Experimental Research ◽  
Hazard Assessment ◽  
Current Knowledge ◽  
Early History ◽  
Assessment Practices ◽  
Related Research ◽  
Systematic Effort ◽  
History Of ◽  
Scientific Fields

Despite the long history of hormesis-related experimental research no systematic effort to describe its early history has been undertaken. The present paper attempts to reconstruct and assess the early history of such research and to evaluate how advances in related scientific fields affected the course of hormesis-related research. The purpose of this paper is not only to satisfy this gap in current knowledge, but also to provide a foundation for the assessment of how the concept of hormetic dose-response relationships may have affected the nature of the bioassay especially with respect to hazard assessment practices within a modern risk assessment Eramework.

scholarly journals The Oldest Stars as Tracers of Heavy Element Formation at Early Epochs

2001 ◽  
Vol 204 ◽  
pp. 333-334 ◽  
Author(s):  
James W. Truran
Keyword(s):  
Star Formation ◽  
Theoretical Models ◽  
Elemental Abundance ◽  
Agb Stars ◽  
Lower Mass ◽  
Set Constraints ◽  
Abundance Patterns ◽  
History Of ◽  
R Process ◽  
Process Elements

Elemental abundance patterns in very metal-poor halo field stars and globular cluster stars play a crucial role both in guiding theoretical models of nucleosynthesis and in providing constraints upon the early star formation and concomitant nucleosynthesis history of our Galaxy. The abundance patterns characterizing the oldest and most metal deficient stars ([Fe/H] ≤ −3) are entirely consistent with their being products of metal-poor massive stars of lifetimes τ ≤ 108years. This includes both the elevated abundances of thealpha-elements (O, Mg, Si, S, Ca, and Ti) relative to iron-peak elements and the dominance of r-process elements over s-process elements. The nucleosynthetic contributions of lower mass AGB stars of longer lifetimes (τ ≈ 109years) begin to appear at metallicities [Fe/H] ≈ −2.5, while clear evidence for iron-peak nuclei produced in supernovae Ia (τ ≥ 1-2x109years?) does not appear until metallicities approaching [Fe/H] ~ −1. Similar trends are also suggested by abundances determined for gas clouds at high redshifts. We review the manner in which a knowledge of the abundances of the stellar and gas components of early populations, as a function of [Fe/H], time, and/or redshift, can be used to set constraints on their star formation and nucleosynthesis histories.

scholarly journals Chemical Evolution and Extremely Metal-Poor Stars

1998 ◽  
Vol 11 (1) ◽  
pp. 49-52
Author(s):  
Andrew McWilliam
Keyword(s):  
Neutron Capture ◽  
Heavy Element ◽  
Massive Stars ◽  
Small Sample ◽  
Heavy Elements ◽  
High Mass ◽  
Type Ii ◽  
Element Abundances ◽  
Halo Stars ◽  
R Process

Early abundance studies (e.g. Pagel 1968) showed that neutron-capture heavy elements (Z > 30) are present in halo stars, but deficient relative iron. Truran (1981) argued that at low [Fe/H] the chemical enrichment time scale was shorter than the lifetime of low-mass AGB progenitors, which are the main source of solar system heavy elements. He proposed that in the halo the heavy elements were produced by high mass stars, in type II supernova events (SNII), by rapid neutron capture nucleosynthesis (the r-process). Spite & Spite (1978) investigated the trend of heavy element abundances with metallicity, from a small sample of halo stars. They found that at [Fe/H]~ -1.5 the halo [heavy element/Fe] ratio is approximately solar; but at lower [Fe/H] there is a roughly linear decrease of [heavy element/Fe] with declining [Fe/H]. Subsequent observations confirmed the general trend of heavy elements in the halo: [M/Fe]~0 down to [Fe/H]~ -2, followed by a linear decline in [M/Fe] to lower [Fe/H] (e.g. Gilroy et al 1988, Lambert 1987). Additional evidence for the role of SNII in halo heavy element synthesis comes from the trend of [Eu/Fe] with [Fe/H]. Europium is an almost pure r-process element (Käppeler et al. 1989) and its abundance trend with metallicity is similar to the α element trend (e.g. O and Mg made in massive stars). The element ratios show an increase in [M/Fe] as [Fe/H] decreases from 0 to —1; below this point [Eu/Fe] and [α/Fe] remain constant at ~+0.3 dex. For α elements this behavior is thought to be due to the change in the relative contributions from type II SN and type la SN in the disk and halo (Tinsley 1979). The trend for Eu also indicates production by massive stars (e.g. SNII). Near [Fe/H]~ -2.5 Eu appears to decline relative to [Fe/H] (like other heavy elements, but unlike the α elements). This abundance trend has been used to constrain the numerous proposed astrophysical sites of the r-process (e.g. Mathews & Cowan 1990).

Re-examining the early history of the Leiden jar: Stabilization and variation in transforming a phenomenon into a fact

2018 ◽  
Vol 56 (3) ◽  
pp. 314-342 ◽  
Author(s):  
Cibelle Celestino Silva ◽  
Peter Heering
Keyword(s):  
Knowledge Production ◽  
Current Knowledge ◽  
Early Period ◽  
Electrical Circuit ◽  
Early History ◽  
Primary Sources ◽  
New Device ◽  
Scientific Knowledge Production ◽  
History Of

In this paper, we examine the period that immediately followed the invention of the Leiden jar. Historians of science have developed narrations that emphasize the role of grounding during the process of charging the jar. In this respect, this episode shows significant aspects that can be used to characterize science, scientific knowledge production, and the nature of science. From our own experimentation, we learned that grounding was not necessary in order to produce the effect. These experiences inspired us to go back to primary sources. In doing so, we came to a new understanding of the early period after Kleist’s and Musschenbroek’s initial creation of the effect. From our analysis, we conclude that it is not the grounding which was perceived as a major innovation (as well as a challenge) during this early period of the discussion but the concept of an electrical circuit. This understanding was fundamental in characterizing the Leiden jar as a new device challenging the then current knowledge of experimental practices in the field of electricity.

scholarly journals S-Process Deficiencies in Low-Mass Supergiant Variables

1989 ◽  
Vol 106 ◽  
pp. 154-154
Author(s):  
Howard E. Bond ◽  
R. Earle Luck
Keyword(s):  
Variable Stars ◽  
Elemental Abundance ◽  
Type Ii ◽  
Hydrogen Burning ◽  
Halo Stars ◽  
Low Mass ◽  
R Process ◽  
Nuclear Processing ◽  
Halo Population ◽  
Process Elements

We have carried out abundance analyses of four low-mass supergiant variable stars (the RV Tauri or RV Tau-like variables AI Cmi, RU Cen, and U Mon, and the Type II Cepheid Kappa Pav) and two Population I Cepheids (CO Aur and V378 Cen). We used model atmospheres in which hydrostatic equilibrium, plane-parallel geometry, and local thermodynamic equilibrium (LTE) were assumed. Discussion of the results, and of published analyses of additional low-mass variables, leads to the following conclusions. (1) The Population I Cepheids show normal, solar elemental abundance ratios (except for the CNO elements, which have been altered by hydrogen burning), lending some support to the validity of the above assumptions for analyses of luminous variable stars. (2) The low-mass variables show metallicities ranging from solar down to [Fe/H] values typical of thick-disk and, in a few cases, of halo stars. (3) Most low-mass variables show a systematic underabundance of the heavy s- and r-process elements. In a few cases this may indicate that the stars were initially of extremely low metal content, and are now hydrogen deficient. However, most of the variables do not appear to belong to the halo population, nor do they show other abundance patterns seen in halo stars. The origin of these underabundances, and their apparent confinement to luminous variables, are difficult to understand in the context of nuclear processing. (4) The heavy-element underabundances correlate with second ionization potential in a manner suggesting that they are non-LTE phenomenan arising from overionization by Lyman-continuum photons. Why a similar effect is not seen in Population I Cepheids is unclear, but may be related to their generally weaker hydrogen emission. (5) Several low-mass variables, including RU Cen and V553 Cen, show carbon enhancements and solar s-process abundances. Relative to the majority of the Type II variables, these stars are s-process enhanced, and we argue that they are related to the Ba II and CH stars.

scholarly journals Globular Clusters and Field Halo Stars

1988 ◽  
Vol 126 ◽  
pp. 133-148
Author(s):  
Bruce W. Carney
Keyword(s):  
Distribution Function ◽  
Globular Clusters ◽  
Chemical Properties ◽  
Elemental Abundance ◽  
Stellar Kinematics ◽  
Halo Stars ◽  
Abundance Patterns ◽  
Halo Population ◽  
Metallicity Distribution ◽  
And Chemical Properties

Recent work on the chemistry and kinematics of the field halo population stars is reviewed, including the metallicity distribution function, elemental abundance patterns, primordial abundances, and their relations with stellar kinematics. The important role played by these stars in determining the ages of the globular clusters is discussed. A comparison is made between the kinematic and chemical properties of the field and cluster stars to ascertain if they share a common history.

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.

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