Galactic Evolution of the Light Elements: A New Set of B Observations

1998 ◽  
pp. 161-166
Author(s):  
F. Primas
Keyword(s):  
Galactic Evolution ◽  
Light Elements

scholarly journals Abundances of the Very Light Elements (D, 3He, 4He and 7LI) And Primordial Nucleosynthesis

1986 ◽  
Vol 7 ◽  
pp. 377-382
Author(s):  
Jean Audouze
Keyword(s):  
Small Groups ◽  
Big Bang ◽  
Galactic Evolution ◽  
Light Elements ◽  
Big Bang Nucleosynthesis ◽  
Primordial Nucleosynthesis ◽  
Groups Of Galaxies

AbstractThe determinations of the primordial abundances of D, 3He, 4He and 7Li play a major role in building up models of Big Bang nucleosynthesis. Much progress has been made recently in that respect but there are still large uncertainties on these determinations. Although canonical Big Bang models predicting a cosmological baryonic parameter ΩB ~ 0.10 consistent with the dynamics of small groups of galaxies and three different families of neutrinos seem to be the most appropriate in accounting for these abundances, the simplest models of galactic evolution lead to discrepant comparisons concerning D and 4He. The relatively small abundance of 4He might challenge the canonical Big Bang models unless specific models of galactic evolution are invoked.

Galactic Evolution and the Formation of the Light Elements

1974 ◽  
Vol 192 ◽  
pp. 487 ◽  
Author(s):  
Jean Audouze ◽  
Beatrice M. Tinsley
Keyword(s):  
Galactic Evolution ◽  
Light Elements

scholarly journals On the Origin of the Light Elements (D, 3He, 4He and 7Li)

1987 ◽  
Vol 124 ◽  
pp. 89-117 ◽  
Author(s):  
Jean Audouze
Keyword(s):  
Phase Transitions ◽  
High Energy ◽  
Galactic Evolution ◽  
Light Elements ◽  
Canonical Models ◽  
Hadron Phase ◽  
Baryonic Density ◽  
Recent Developments ◽  
Quark Nuggets ◽  
The Universe

The abundances of the very light elements (D, 3He, 4He and 7Li) constitute indeed one of the most powerful constraints in cosmology: they are known to fix very interesting limits on the baryonic density of the Universe and on the maximum number of neutrino (lepton) families in the frame of the simplest canonical models. Given the importance of these predictions, these models should be analysed very cautiously at the light of recent developments in the observations of these elements. In order to make the simplest models consistent with the observations, it is argued that a thorough destruction of D should occur during the galactic evolution. Moreover this review deals also with some models invoking the possible existence of massive unstable neutrinos, gravitinos or photinos which would decay into high energy photons or of quark nuggets which could be created during the quark-hadron phase transitions. Such models have been designed in an attempt to overcome the limitation on the Universe density coming from these abundance determinations. Although the simple canonical models are especially attractive such models cannot be disregarded.

scholarly journals The Pre - Main Sequence

1993 ◽  
Vol 137 ◽  
pp. 395-409
Author(s):  
Francesca D’Antona
Keyword(s):  
Thermal Equilibrium ◽  
Main Sequence ◽  
Age Determination ◽  
Galactic Evolution ◽  
Light Elements ◽  
Large Uncertainty ◽  
Nuclear Burning ◽  
Low Mass ◽  
Late Stages

AbstractThe Pre-Main-Sequence (pre-MS) is defined as the phase following the protostellar stage and ending with the ignition of hydrogen in the stellar core. Models in hydrostatic and thermal equilibrium such as typical “Hayashi track” models are basically adequate to describe the internal structure of pre-MS stars, although for a fraction of pre-MS objects there can be phases of accretion also at late stages, which may influence the surface abundances of light elements.The interior evolution of pre-MS structures is focused in the two main stages’ of Deuterium and Lithium burning for the low mass (M ≤ 1.5M⊙) stars. The location in the HR diagram of theoretical tracks is still subject to large uncertainty, even more apparent today that new opacities and treatment of turbulent convection are available, and the results can be internally compared. Uncertainties amount to a factor ~ two for mass and age determination of individual objects, and affect the absolute location for both the D-burning and the Li-burning regions. Qualitative constraints, such as that there can not be Li-depletion at L ≥ L⊙, remain valid. Abundances of7Li at the surface of pre-MS stars, if measured at a stage which can definitely be considered previous to the possible occurrence of nuclear burning, and, consequently, previous to other depletion mechanism which may occur later on, provide constraints on galactic evolution of this element of cosmological interest.

scholarly journals First stars VI – Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements

2005 ◽  
Vol 430 (2) ◽  
pp. 655-668 ◽  
Author(s):  
M. Spite ◽  
R. Cayrel ◽  
B. Plez ◽  
V. Hill ◽  
F. Spite ◽  
...  
Keyword(s):  
Galactic Evolution ◽  
Light Elements ◽  
First Stars

Scattering-angle dependence of signal/background ratio of inner-shell electron excitation loss in EELS

1983 ◽  
Vol 41 ◽  
pp. 390-391
Author(s):  
T. Oikawa ◽  
M. Inoue ◽  
T. Honda ◽  
Y. Kokubo
Keyword(s):  
Energy Loss ◽  
Electron Excitation ◽  
Heavy Elements ◽  
Background Intensity ◽  
Light Elements ◽  
Energy Analyzer ◽  
High Background ◽  
Scattering Angle ◽  
Angle Dependence ◽  
Shell Electron

EELS allows us to make analysis of light elements such as hydrogen to heavy elements of microareas on the specimen. In energy loss spectra, however, elemental signals ride on a high background; therefore, the signal/background (S/B) ratio is very low in EELS. A technique which collects the center beam axial-symmetrically in the scattering angle is generally used to obtain high total intensity. However, the technique collects high background intensity together with elemental signals; therefore, the technique does not improve the S/B ratio. This report presents the experimental results of the S/B ratio measured as a function of the scattering angle and shows the possibility of the S/B ratio being improved in the high scattering angle range.Energy loss spectra have been measured using a JEM-200CX TEM with an energy analyzer ASEA3 at 200 kV.Fig.l shows a typical K-shell electron excitation edge riding on background in an energy loss spectrum.

Quantitative EPMA of nitrogen : A tricky element in the electron-probe microanalyzer

1992 ◽  
Vol 50 (2) ◽  
pp. 1622-1623
Author(s):  
G.F. Bastin ◽  
H.J.M. Heijligers
Keyword(s):  
Background Subtraction ◽  
Electron Probe ◽  
Detection System ◽  
Higher Order ◽  
Light Elements ◽  
Strong Suppression ◽  
Electron Probe Microanalyzer ◽  
Quantitative Epma ◽  
Peak Count ◽  
Lead Stearate

Among the ultra-light elements B, C, N, and O nitrogen is the most difficult element to deal with in the electron probe microanalyzer. This is mainly caused by the severe absorption that N-Kα radiation suffers in carbon which is abundantly present in the detection system (lead-stearate crystal, carbonaceous counter window). As a result the peak-to-background ratios for N-Kα measured with a conventional lead-stearate crystal can attain values well below unity in many binary nitrides . An additional complication can be caused by the presence of interfering higher-order reflections from the metal partner in the nitride specimen; notorious examples are elements such as Zr and Nb. In nitrides containing these elements is is virtually impossible to carry out an accurate background subtraction which becomes increasingly important with lower and lower peak-to-background ratios. The use of a synthetic multilayer crystal such as W/Si (2d-spacing 59.8 Å) can bring significant improvements in terms of both higher peak count rates as well as a strong suppression of higher-order reflections.

Utilization of the nuclear energy of the light elements

1991 ◽  
Vol 161 (5) ◽  
pp. 171-175 ◽  
Author(s):  
Yu.B. Khariton ◽  
Ya.B. Zeldovich ◽  
I.I. Gurevich ◽  
I.Ya. Pomeranchuk
Keyword(s):  
Nuclear Energy ◽  
Light Elements
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