73 research outputs found
Co-production of light p-, s- and r-process isotopes in the high-entropy wind of type II supernovae
We have performed large-scale nucleosynthesis calculations within the
high-entropy-wind (HEW) scenario of type II supernovae. The primary aim was to
constrain the conditions for the production of the classical "p-only" isotopes
of the light trans-Fe elements. We find, however, that for electron fractions
in the range 0.458 Y 0.478, sizeable abundances of p-, s- and
r-process nuclei between Zn and Ru are coproduced in the HEW at
low entropies (S 100) by a primary charged-particle process after an
-rich freezeout. With the above Y -- S correlation, most of the
predicted isotopic abundance ratios within a given element (e.g.
Zn(p)/Zn(r) or Mo(p)/Mo(p)), as well as of
neighboring elements (e.g. Ge(s+p)/Se(p) or
Se(p)/Kr(p)) agree with the observed Solar-System ratios. Taking
the Mo isotopic chain as a particularly challenging example, we show that our
HEW model can account for the production of all 7 stable isotopes, from
"p-only" Mo, via "s-only" Mo up to "r-only" Mo.
Furthermore, our model is able to reproduce the isotopic composition of Mo in
presolar SiC X-grains.}Comment: 10 pages, 2 figure
Charged-Particle and Neutron-Capture Processes in the High-Entropy Wind of Core-Collapse Supernovae
The astrophysical site of the r-process is still uncertain, and a full
exploration of the systematics of this process in terms of its dependence on
nuclear properties from stability to the neutron drip-line within realistic
stellar environments has still to be undertaken. Sufficiently high neutron to
seed ratios can only be obtained either in very neutron-rich low-entropy
environments or moderately neutron-rich high-entropy environments, related to
neutron star mergers (or jets of neutron star matter) and the high-entropy wind
of core-collapse supernova explosions. As chemical evolution models seem to
disfavor neutron star mergers, we focus here on high-entropy environments
characterized by entropy , electron abundance and expansion velocity
. We investigate the termination point of charged-particle reactions,
and we define a maximum entropy for a given and ,
beyond which the seed production of heavy elements fails due to the very small
matter density. We then investigate whether an r-process subsequent to the
charged-particle freeze-out can in principle be understood on the basis of the
classical approach, which assumes a chemical equilibrium between neutron
captures and photodisintegrations, possibly followed by a -flow
equilibrium. In particular, we illustrate how long such a chemical equilibrium
approximation holds, how the freeze-out from such conditions affects the
abundance pattern, and which role the late capture of neutrons originating from
-delayed neutron emission can play.Comment: 52 pages, 31 figure
Nucleosynthesis in the Early Galaxy
Recent observations of r-process-enriched metal-poor star abundances reveal a
non-uniform abundance pattern for elements . Based on non-correlation
trends between elemental abundances as a function of Eu-richness in a large
sample of metal-poor stars, it is shown that the mixing of a consistent and
robust light element primary process (LEPP) and the r-process pattern found in
r-II metal-poor stars explains such apparent non-uniformity. Furthermore, we
derive the abundance pattern of the LEPP from observation and show that it is
consistent with a missing component in the solar abundances when using a recent
s-process model. As the astrophysical site of the LEPP is not known, we explore
the possibility of a neutron capture process within a site-independent
approach. It is suggested that scenarios with neutron densities
or in the range best
explain the observations.Comment: 28 pages, 7 Postscript figures. To be published in The Astrophysical
Journa
The Hamburg/ESO R-process Enhanced Star survey (HERES) IV. Detailed abundance analysis and age dating of the strongly r-process enhanced stars CS 29491-069 and HE 1219-0312
We report on a detailed abundance analysis of two strongly r-process
enhanced, very metal-poor stars newly discovered in the HERES project, CS
29491-069 ([Fe/H]=-2.51, [r/Fe]=+1.1) and HE 1219-0312 ([Fe/H]=-2.96,
[r/Fe]=+1.5). The analysis is based on high-quality VLT/UVES spectra and MARCS
model atmospheres. We detect lines of 15 heavy elements in the spectrum of CS
29491-069, and 18 in HE 1219-0312; in both cases including the Th II 4019 {\AA}
line. The heavy-element abundance patterns of these two stars are mostly
well-matched to scaled solar residual abundances not formed by the s-process.
We also compare the observed pattern with recent high-entropy wind (HEW)
calculations, which assume core-collapse supernovae of massive stars as the
astrophysical environment for the r-process, and find good agreement for most
lanthanides. The abundance ratios of the lighter elements strontium, yttrium,
and zirconium, which are presumably not formed by the main r-process, are
reproduced well by the model. Radioactive dating for CS 29491-069 with the
observed thorium and rare-earth element abundance pairs results in an average
age of 9.5 Gyr, when based on solar r-process residuals, and 17.6 Gyr, when
using HEW model predictions. Chronometry seems to fail in the case of HE
1219-0312, resulting in a negative age due to its high thorium abundance. HE
1219-0312 could therefore exhibit an overabundance of the heaviest elements,
which is sometimes called an "actinide boost"
DIAGNOSTIC BIOLOGIQUE DE LA BRUCELLOSE HUMAINE: COMPARAISON DE DEUX TECHNIQUES DE SEROAGGLUTINATION
objective: Evaluate the technical characteristics of two agglutination techniques used for the detection of serum antibodies of Brucella. Material and methods: The search for Brucella antibodies was performed in 100 serum samples. They come from patients with brucellosis was suspected on clinical and epidemiological criteria. The average age was 31 years with a standard deviation of 1.5 and a sex ratio (M / W) is equal to 2. The two methods used are (manual): 1- BRUCELLACAPT® (Vircell,Spain) 2- ROSE BENGAL ® (Bio-Rad, France). Results: The results showed a concordance between the two techniques of 92% (80% negative results and 12% positive), and discrepancy of 8%. Conclusion: Discordant results demonstrate the need to always integrate the approach diagnostic of a clinical and epidemiological data associated with biological data, and secondly, to take into account the threshold value of detection of serological markers of the technique used.Objectif : Evaluer les caractéristiques de deux techniques de séroagglutination pour la détection des anticorps sériques anti-Brucella. Matériel et méthodes : La recherche des anticorps anti Brucella a été effectuée sur 100 échantillons de sérums, provenant de patients chez qui la brucellose a été suspectée sur des critères cliniques et épidémiologiques. La moyenne d’âge est de 31 ans avec un écart type de 1,5 et un sex-ratio (H/F) de 2. Les deux méthodes de séroagglutination utilisées (manuelles) sont : 1- BRUCELLACAPT® (Vircell,Espagne) 2- ROSE BENGALE® (Bio Rad, France). Résultats : Les résultats ont montré une concordance entre les deux techniques de 92% (80% négatifs et 12% positifs), et une disconcordance de 8%. Conclusion : Les résultats discordants démontrent la nécessité d’intégrer à la démarche diagnostic, les données cliniques, épidémiologiques, l’évolution de la maladie, ainsi que les données biologiques et de prendre en considération la valeur seuil de détection des marqueurs sérologiques de la technique utilisée
COMPARAISON DE DEUX TECHNIQUES IMMUNOENZYMATIQUES ELISA POUR LA DETECTION DES ANTICORPS IgG SERIQUES ANTIRUBEOLIQUES
OBJECTIF: Il s’agit d’évaluer les caractéristiques de deux techniques immunoenzymatiques ELISA (principe, performances et limites) pour la détection des IgG sériques antirubéolique. MATERIEL ET METHODES: L a recherche des IgG antirubéoliques a été effectuée dans 100 échantillons de sérums recueillis dans le laboratoire d’immunosérologie du CHU Ibn Rochd de Casablanca. Ils proviennent de patients hospitalisés et de consultants externes du CHU. Il s’agit pour la plupart de jeunes femmes (85%) et de nouveaux nés (12%). Les deux méthodes immunoenzymatiques ELISA utilisées sont : 1- kit Vircell®Spain (technique manuelle) 2- AxsymAbbott®USA (technique microparticulaire automatisée). RESULTATS: Les résultats sérologiques pour la détection des anticorps IgG antirubéolique ont montré une concordance entre les deux techniques de 94% (90% des résultats positifs et 4% négatifs et une discordance de 6%. CONCLUSION: Même si la concordance entre les deux techniques est de 94%, les résultats discordants démontrent la nécessité d’intégrer toujours la démarche diagnostique, d’une part les données cliniques associées aux données biologiques, et d‘autres part, de prendre en considération la valeur seuil de détection des marques sérologiques spécifiques de la technique utilisée, ainsi que la qualité des échantillons testés
Nucleosynthesis Modes in the High-Entropy-Wind of Type II Supernovae: Comparison of Calculations with Halo-Star Observations
While the high-entropy wind (HEW) of Type II supernovae remains one of the
more promising sites for the rapid neutron-capture (r-) process, hydrodynamic
simulations have yet to reproduce the astrophysical conditions under which the
latter occurs. We have performed large-scale network calculations within an
extended parameter range of the HEW, seeking to identify or to constrain the
necessary conditions for a full reproduction of all r-process residuals
N_{r,\odot}=N_{\odot}-N_{s,\odot} by comparing the results with recent
astronomical observations. A superposition of weighted entropy trajectories
results in an excellent reproduction of the overall N_{r,\odot}-pattern beyond
Sn. For the lighter elements, from the Fe-group via Sr-Y-Zr to Ag, our HEW
calculations indicate a transition from the need for clearly different sources
(conditions/sites) to a possible co-production with r-process elements,
provided that a range of entropies are contributing. This explains recent
halo-star observations of a clear non-correlation of Zn and Ge and a weak
correlation of Sr - Zr with heavier r-process elements. Moreover, new
observational data on Ru and Pd seem to confirm also a partial correlation with
Sr as well as the main r-process elements (e.g. Eu).Comment: 15 pages, 1 table, 4 figures; To be published in the Astrophysical
Journal Letter
The influence of collective neutrino oscillations on a supernova r-process
Recently, it has been demonstrated that neutrinos in a supernova oscillate
collectively. This process occurs much deeper than the conventional
matter-induced MSW effect and hence may have an impact on nucleosynthesis. In
this paper we explore the effects of collective neutrino oscillations on the
r-process, using representative late-time neutrino spectra and outflow models.
We find that accurate modeling of the collective oscillations is essential for
this analysis. As an illustration, the often-used "single-angle" approximation
makes grossly inaccurate predictions for the yields in our setup. With the
proper multiangle treatment, the effect of the oscillations is found to be less
dramatic, but still significant. Since the oscillation patterns are sensitive
to the details of the emitted fluxes and the sign of the neutrino mass
hierarchy, so are the r-process yields. The magnitude of the effect also
depends sensitively on the astrophysical conditions - in particular on the
interplay between the time when nuclei begin to exist in significant numbers
and the time when the collective oscillation begins. A more definitive
understanding of the astrophysical conditions, and accurate modeling of the
collective oscillations for those conditions, is necessary.Comment: 27 pages, 10 figure
Characterizing the Chemistry of the Milky Way Stellar Halo: Detailed Chemical Analysis of a Metal-Poor Stellar Stream
We present the results of a detailed abundance analysis of one of the
confirmed building blocks of the Milky Way stellar halo, a
kinematically-coherent metal-poor stellar stream. We have obtained high
resolution and high S/N spectra of 12 probable stream members using the MIKE
spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the
2dCoude spectrograph on the Smith Telescope at McDonald Observatory. We have
derived abundances or upper limits for 51 species of 46 elements in each of
these stars. The stream members show a range of metallicity (-3.4 < [Fe/H] <
-1.5) but are otherwise chemically homogeneous, with the same star-to-star
dispersion in [X/Fe] as the rest of the halo. This implies that, in principle,
a significant fraction of the Milky Way stellar halo could have formed from
accreted systems like the stream. The stream stars show minimal evolution in
the alpha or Fe-group elements over the range of metallicity. This stream is
enriched with material produced by the main and weak components of the rapid
neutron-capture process and shows no evidence for enrichment by the slow
neutron-capture process.Comment: v2: Removed references to M15 after learning that the source
kinematic data for M15 were incorrect in an earlier paper. M15 is not related
to this stream. (ApJ, accepted; 31 pages, 18 figures, 11 tables
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