1,604 research outputs found
Pre-suprenova evolution of rotating massive stars
The Geneva evolutionary code has been modified to study the advanced stages
(Ne, O, Si burnings) of rotating massive stars. Here we present the results of
four 20 solar mass stars at solar metallicity with initial rotational
velocities of 0, 100, 200 and 300 km/s in order to show the crucial role of
rotation in stellar evolution. As already known, rotation increases mass loss
and core masses (Meynet and Maeder 2000). A fast rotating 20 solar mass star
has the same central evolution as a non-rotating 26 solar mass star. Rotation
also increases strongly net total metal yields. Furthermore, rotation changes
the SN type so that more SNIb are predicted (see Meynet and Maeder 2003 and N.
Prantzos and S. Boissier 2003). Finally, SN1987A-like supernovae progenitor
colour can be explained in a single rotating star scenario.Comment: To appear in proceedings of IAU Colloquium 192, "Supernovae (10 years
of 1993J)", Valencia, Spain 22-26 April 2003, eds. J.M. Marcaide, K.W.
Weiler, 5 pages, 8 figure
Neutrino Nucleosynthesis of radioactive nuclei in supernovae
We study the neutrino-induced production of nuclides in explosive supernova
nucleosynthesis for progenitor stars with solar metallicity and initial main
sequence masses between 15 M and 40 M. We improve previous
investigations i) by using a global set of partial differential cross sections
for neutrino-induced charged- and neutral-current reactions on nuclei with
charge numbers and ii) by considering modern supernova neutrino
spectra which have substantially lower average energies compared to those
previously adopted in neutrino nucleosynthesis studies. We confirm the
production of Li, B, La, and Ta by neutrino
nucleosynthesis, albeit at slightly smaller abundances due to the changed
neutrino spectra. We find that for stars with a mass smaller than 20 M,
F is produced mainly by explosive nucleosynthesis while for higher mass
stars it is produced by the process. We also find that neutrino-induced
reactions, either directly or indirectly by providing an enhanced abundance of
light particles, noticeably contribute to the production of the radioactive
nuclides Na and Al. Both nuclei are prime candidates for
gamma-ray astronomy. Other prime targets, Ti and Fe, however, are
insignificantly produced by neutrino-induced reactions. We also find a large
increase in the production of the long-lived nuclei Nb and Tc due
to charged-current neutrino capture.Comment: 6 pages, 2 figures, 2 table
Stellar evolution with rotation XIII: Predicted GRB rates at various Z
We present the evolution of rotation in models of massive single stars
covering a wide range of masses and metallicities. These models reproduce very
well observations during the early stages of the evolution (in particular WR
populations and ratio between type II and type Ib,c at different metallicities,
see Meynet & Maeder 2005).
Our models predict the production of fast rotating black holes. Models with
large initial masses or high metallicity end their life with less angular
momentum in their central remnant with respect to the break-up limit for the
remnant. Many WR star models satisfy the three main criteria (black hole
formation, loss of hydrogen-rich envelope and enough angular momentum to form
an accretion disk around the black hole) for gamma-ray bursts (GRB) production
via the collapsar model (Woosley 1993). Considering all types of WR stars as
GRB progenitors, there would be too many GRBs compared to observations. If we
consider only WO stars (type Ic supernovae as is the case for
SN2003dh/GRB030329, see Matheson et al. 2003) as GRBs progenitors, the GRBs
production rates are in much better agreement with observations. WO stars are
produced only at low metallicities in the present grid of models. This
prediction can be tested by future observations.Comment: ~16 pages, 14 figures, accepted by A&
Nucleosynthesis in Massive Stars With Improved Nuclear and Stellar Physics
We present the first calculations to follow the evolution of all stable
nuclei and their radioactive progenitors in stellar models computed from the
onset of central hydrogen burning through explosion as Type II supernovae.
Calculations are performed for Pop I stars of 15, 19, 20, 21, and 25 M_sun
using the most recently available experimental and theoretical nuclear data,
revised opacity tables, neutrino losses, and weak interaction rates, and taking
into account mass loss due to stellar winds. A novel ``adaptive'' reaction
network is employed with a variable number of nuclei (adjusted each time step)
ranging from about 700 on the main sequence to more than 2200 during the
explosion. The network includes, at any given time, all relevant isotopes from
hydrogen through polonium (Z=84). Even the limited grid of stellar masses
studied suggests that overall good agreement can be achieved with the solar
abundances of nuclei between 16O and 90Zr. Interesting discrepancies are seen
in the 20 M_sun model and, so far, only in that model, that are a consequence
of the merging of the oxygen, neon, and carbon shells about a day prior to core
collapse. We find that, in some stars, most of the ``p-process'' nuclei can be
produced in the convective oxygen burning shell moments prior to collapse; in
others, they are made only in the explosion. Serious deficiencies still exist
in all cases for the p-process isotopes of Ru and Mo.Comment: 53 pages, 17 color figures (3 as separate GIF images), slightly
extended discussion and references, accepted by Ap
Ueber die strukturellen Phasenuebergaenge von perowskitaehnlichen Schichtenstrukturen vom Typ (C(sub n)H(sub 2n+1)NHâ)âMeClâ
Control program of the neutron four-circle-diffractometer P110 at the ORPHEE reactor/CEN Saclay
Neutral-current neutrino reactions in the supernova environment
We study the neutral-current neutrino scattering for four nuclei in the iron
region. We evaluate the cross sections for the relevant temperatures during the
supernova core collapse and derive Gamow-Teller distributions from large-scale
shell-model calculations. We show that the thermal population of the excited
states significantly enhances the cross sections at low neutrino energies.
Calculations of the outgoing neutrino spectra indicate the prospect of neutrino
upscattering at finite temperatures. Both results are particularly notable in
even-even nuclei.Comment: 14 pages, 4 figures, accepted in Phys. Lett. B
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