591 research outputs found
Lithium-Beryllium-Boron Evolution: From Meneguzzi, Audouze and Reeves 1971 Up to Now
We review the main sources of LiBeB production and show that a primary
mechanism is at work in the early Galaxy involving both ejection and
acceleration of He, C and O at moderate energy, which by nuclear interaction
with
H and He produce light isotopes. The precise measurement of the Be abundance
at [Fe/H] = -3.3 and of in halo stars find an explanation in this
framework. Thus, the preservation of in the atmosphere of metal poor
stars implied, points toward the fact the Spite plateau reflects the primordial
value of Li. Consequently, it can be used as a baryodensitometer.Comment: 6 pages, no figure, invited talk, to be published in World
Scientific, Proceedings of the conference "Cosmic Evolution" in the honor of
Jean Audouze and James W. Truran, held at the Institut d'Astrophysique de
Paris, Franc
Updated constraint on a primordial magnetic field during big bang nucleosynthesis and a formulation of field effects
A new upper limit on the amplitude of primordial magnetic field (PMF) is
derived by a comparison between a calculation of elemental abundances in big
bang nucleosynthesis (BBN) model and the latest observational constraints on
the abundances. Updated nuclear reaction rates are adopted in the calculation.
Effects of PMF on the abundances are consistently taken into account in the
numerical calculation with the precise formulation of changes in physical
variables. We find that abundances of 3He and 6Li increase while that of 7Li
decreases when the PMF amplitude increases, in the case of the baryon-to-photon
ratio determined from the measurement of cosmic microwave background radiation.
We derive a constraint on the present amplitude of PMF, i.e., B(0)<1.5 micro G
[corresponding to the amplitude less than 2.0x10^{11} G at BBN temperature of
T=10^9 K] based on the rigorous calculation.Comment: 26 pages, 4 figures, new observation of D/H ratio adopted, tighter
constraint derived, Sec. IV modified, accepted for publication in PR
LiBeB, Cosmic Rays and Gamma-Ray Line Astronomy
This article is a summary of a recently held conference on the light
elements, Li, Be and B, and their relationship to cosmic-ray origin and
gamma-ray astronomy. The proceedings will be published by the PASP.Comment: latex 6 pages, uses aasms4.sty To appear in the Publications of the
Astronomical Society of the Pacific (PASP
Constitutional Law - Equal Protection - Affirmative Action Programs - Reverse Discrimination
The Supreme Court of Washington has held that the University of Washington Law School may, without any showing of past discriminatory practices on its part, apply separate and distinct admissions criteria to its minority applicants in order to achieve a racial balance within the school.
DeFunis v. Odegaard, 82 Wash. 2d 11, 507 P.2d 1169, cert. granted, 94 S. Ct. 538 (1973)
Testing Spallation Processes With Beryllium and Boron
The nucleosynthesis of Be and B by spallation processes provides unique
insight into the origin of cosmic rays. Namely, different spallation schemes
predict sharply different trends for the growth of LiBeB abundances with
respect to oxygen. ``Primary'' mechanisms predict BeB O, and are well
motivated by the data if O/Fe is constant at low metallicity. In contrast,
``secondary'' mechanisms predict BeB O and are consistent with
the data if O/Fe increases towards low metallicity as some recent data suggest.
Clearly, any primary mechanism, if operative, will dominate early in the
history of the Galaxy. In this paper, we fit the BeB data to a two-component
scheme which includes both primary and secondary trends. In this way, the data
can be used to probe the period in which primary mechanisms are effective. We
analyze the data using consistent stellar atmospheric parameters based on
Balmer line data and the continuum infrared flux. Results depend sensitively on
Pop II O abundances and, unfortunately, on the choice of stellar parameters.
When using recent results which show O/Fe increasing toward lower metallicity,
a two-component Be-O fits indicates that primary and secondary components
contribute equally at [O/H] = -1.8 for Balmer line data; and
[O/H] = -1.4 to -1.8 for IRFM. We apply these constraints to recent
models for LiBeB origin. The Balmer line data does not show any evidence for
primary production. On the other hand, the IRFM data does indicate a preference
for a two-component model, such as a combination of standard GCR and
metal-enriched particles accelerated in superbubbles. These conclusions rely on
a detailed understanding of the abundance data including systematic effects
which may alter the derived O-Fe and BeB-Fe relations.Comment: 40 pages including 11 ps figures. Written in AASTe
Can Galactic Cosmic Rays Account for Solar 6Li Without Overproducing Gamma Rays?
Cosmic-ray interactions with interstellar gas produces both 6Li, which
accumulates in the interstellar medium (ISM), and mesons, which decay
to gamma-rays which propagate throughout the cosmos. Local 6Li abundances and
extragalactic gamma-rays thus have a common origin which tightly links them. We
exploit this connection to use gamma-ray observations to infer the contribution
to 6Li nucleosynthesis by standard Galactic cosmic-ray (GCR) interactions with
the ISM. Our calculation uses a carefully propagated cosmic-ray spectrum and
accounts for 6Li production from both fusion reactions () as well as from spallation channels ({p,\alpha+CNO \to ^6Li). We find
that although extreme assumptions yield a consistent picture, more realistic
ones indicate that solar 6Li cannot be produced by standard GCRs alone without
overproducing the hadronic gamma rays. Implications for the primordial 6Li
production by decaying dark matter and cosmic rays from cosmological structure
formation are discussed. Upcoming gamma-ray observations by GLAST will be
crucial for determining the resolution of this problem.Comment: 4 pages, 1 figure To be published in ApJ
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