100 research outputs found
Nucleosynthesis in novae: experimental progress in the determination of nuclear reaction rates
The sources of nuclear uncertainties in nova nucleosynthesis have been
identified using hydrodynamical nova models. Experimental efforts have followed
and significantly reduced those uncertainties. This is important for the
evaluation of nova contribution to galactic chemical evolution, gamma--ray
astronomy and possibly presolar grain studies. In particular, estimations of
expected gamma-ray fluxes are essential for the planning of observations with
existing or future satellites.Comment: Invited contribution to the "Origin of Matter and Evolution of
Galaxies" conference (OMEG07) with additional and color figure
Explosions inside Ejecta and Most Luminous Supernovae
The extremely luminous supernova SN2006gy is explained in the same way as
other SNIIn events: light is produced by a radiative shock propagating in a
dense circumstellar envelope formed by a previous weak explosion. The problems
in the theory and observations of multiple-explosion SNe IIn are briefly
reviewed.Comment: 9 pages, 6 figures, LateX aipproc.cls. A bit more details and color
added to Fig.3. The 10th International Symposium on Origin of Matter and
Evolution of Galaxies (OMEG07), Sapporo, Japan, December 200
Recent Efforts in Data Compilations for Nuclear Astrophysics
Some recent efforts in compiling data for astrophysical purposes are
introduced, which were discussed during a JINA-CARINA Collaboration meeting on
"Nuclear Physics Data Compilation for Nucleosynthesis Modeling" held at the
ECT* in Trento/ Italy from May 29th- June 3rd, 2007. The main goal of this
collaboration is to develop an updated and unified nuclear reaction database
for modeling a wide variety of stellar nucleosynthesis scenarios. Presently a
large number of different reaction libraries (REACLIB) are used by the
astrophysics community. The "JINA Reaclib Database" on
http://www.nscl.msu.edu/\~nero/db/ aims to merge and fit the latest
experimental stellar cross sections and reaction rate data of various
compilations, e.g. NACRE and its extension for Big Bang nucleosynthesis,
Caughlan and Fowler, Iliadis et al., and KADoNiS. The KADoNiS (Karlsruhe
Astrophysical Database of Nucleosynthesis in Stars,
http://nuclear-astrophysics.fzk.de/kadonis) project is an online database for
neutron capture cross sections relevant to the s process. The present version
v0.2 is already included in a REACLIB file from Basel university
(http://download.nucastro.org/astro/reaclib). The present status of
experimental stellar cross sections in KADoNiS is shown. A "high
priority list" for measurements and evaluations for light charged-particle
reactions set up by the JINA-CARINA collaboration is presented. The central web
access point to submit and evaluate new data is provided by the Oak Ridge group
via the http://www.nucastrodata.org homepage. "Workflow tools" aim to make the
evaluation process transparent and allow users to follow the progress.Comment: Proceedings 10th Int. Symp. on Origin of Matter and Evolution of
Galaxies OMEG07, Sapporo/ Japan, December 4-7 200
The Dichotomy of the Halo of the Milky Way
We summarize evidence that the halo of the Milky Way comprises two different,
and broadly overlapping, stellar components. The two structures exhibit
different chemical compositions, spatial distributions, and kinematics. These
results were obtained through an analysis of more than 20,000 calibration stars
from the Sloan Digital Sky Survey (SDSS). The duality of the stellar halo
directly impacts galaxy formation models, for the Milky Way and other large
spirals.Comment: 6 pages, 4 figures, to appear in Proceedings of the OMEG07
Conference, held in December 200
The r-Process in Supersonic Neutrino-Driven Winds: The Roll of Wind Termination Shock
Recent hydrodynamic studies of core-collapse supernovae imply that the
neutrino-heated ejecta from a nascent neutron star develops to supersonic
outflows. These supersonic winds are influenced by the reverse shock from the
preceding supernova ejecta, forming the wind termination shock. We investigate
the effects of the termination shock in neutrino-driven winds and its roll on
the r-process. Supersonic outflows are calculated with a semi-analytic
neutrino-driven wind model. Subsequent termination-shocked, subsonic outflows
are obtained by applying the Rankine-Hugoniot relations. We find a couple of
effects that can be relevant for the r-process. First is the sudden slowdown of
the temperature decrease by the wind termination. Second is the entropy jump by
termination-shock heating, up to several 100NAk. Nucleosynthesis calculations
in the obtained winds are performed to examine these effects on the r-process.
We find that 1) the slowdown of the temperature decrease plays a decisive roll
to determine the r-process abundance curves. This is due to the strong
dependences of the nucleosynthetic path on the temperature during the r-process
freezeout phase. Our results suggest that only the termination-shocked winds
with relatively small shock radii (~500km) are relevant for the bulk of the
solar r-process abundances (A~100-180). The heaviest part in the solar
r-process curve (A~180-200), however, can be reproduced both in shocked and
unshocked winds. These results may help to constrain the mass range of
supernova progenitors relevant for the r-process. We find, on the other hand,
2) negligible roles of the entropy jump on the r-process. This is a consequence
that the sizable entropy increase takes place only at a large shock radius
(~10,000km) where the r-process has already ceased.Comment: 11 pages, 7 figures, submitted to ApJ, revised following referee's
comments,Accepted for publication in Ap
Supernova Nucleosynthesis and Extremely Metal-Poor Stars
We investigate hydrodynamical and nucleosynthetic properties of the
jet-induced explosion of a population III star and compare the
abundance patterns of the yields with those of the metal-poor stars. We
conclude that (1) the ejection of Fe-peak products and the fallback of
unprocessed materials can account for the abundance patterns of the extremely
metal-poor (EMP) stars and that (2) the jet-induced explosion with different
energy deposition rates can explain the diversity of the abundance patterns of
the metal-poor stars. Furthermore, the abundance distribution after the
explosion and the angular dependence of the yield are shown for the models with
high and low energy deposition rates and . We also find that the
peculiar abundance pattern of a Si-deficient metal-poor star HE 1424--0241 can
be reproduced by the angle-delimited yield for of
the model with .Comment: 6 pages, 3 figures. To appear in "ORIGIN OF MATTER AND EVOLUTION OF
GALAXIES: From the Dawn of Universe to the Formation of Solar System", AIP
Conf. Proc. 1016 (December 2007, Sapporo), eds. T. Suda, T. Nozawa, et al.
(Melville: AIP
Observations of Very Metal-Poor Stars in the Galaxy
I report on recent results from observations of stars with metallicities
[Fe/H] <= -2.0. These include a substantial new sample of objects with
high-resolution observations obtained as part of a follow-up of the HK Survey,
The Hamburg/ESO Survey, and the ongoing survey SEGUE: Sloan Extension for
Galactic Understanding and Exploration. Perspectives on the next directions are
also provided.Comment: 8 pages, 4 figures, to appear in Proceedings of OMEG07, a conference
held in December 200
Neutrino Mass Bounds from Neutrinoless Double Beta Decays and Large Scale Structures
We investigate the way how the total mass sum of neutrinos can be constrained
from the neutrinoless double beta decay and cosmological probes with cosmic
microwave background (WMAP 3-year results), large scale structures including
2dFGRS and SDSS data sets. First we discuss, in brief, on the current status of
neutrino mass bounds from neutrino beta decays and cosmic constrain within the
flat model. In addition, we explore the interacting neutrino
dark-energy model, where the evolution of neutrino masses is determined by
quintessence scalar filed, which is responsable for cosmic acceleration today.
Assuming the flatness of the universe, the constraint we can derive from the
current observation is eV at the 95 % confidence level,
which is consistent with eV in the flat
model. Finally we discuss the future prospect of the neutrino mass bound with
weak-lensing effects.Comment: Latex 12 pages, 3 figures, correct typos and add new reference
Multi-Dimensional Simulations of Radiative Transfer in Aspherical Core-Collapse Supernovae
We study optical radiation of aspherical supernovae (SNe) and present an
approach to verify the asphericity of SNe with optical observations of
extragalactic SNe. For this purpose, we have developed a multi-dimensional
Monte-Carlo radiative transfer code, SAMURAI (SupernovA MUlti-dimensional
RAdIative transfer code). The code can compute the optical light curve and
spectra both at early phases (<~ 40 days after the explosion) and late phases
(~ 1 year after the explosion), based on hydrodynamic and nucleosynthetic
models. We show that all the optical observations of SN 1998bw (associated with
GRB 980425) are consistent with polar-viewed radiation of the aspherical
explosion model with kinetic energy 20 x 10^{51} ergs. Properties of off-axis
hypernovae are also discussed briefly.Comment: 6 pages, 4 figures. Proceedings of "Origin of Matter and Evolution of
Galaxies (OMEG07): From the Dawn of Universe to the Formation of Solar
System", 4-7 Dec 2007, Sapporo, Japa
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