48,970 research outputs found
Nuclear Reactions Rates Governing the Nucleosynthesis of Ti44
Large excesses of Ca44 in certain presolar graphite and silicon carbide
grains give strong evidence for Ti44 production in supernovae. Furthermore,
recent detection of the Ti44 gamma-line from the Cas A SNR by CGRO/COMPTEL
shows that radioactive Ti44 is produced in supernovae. These make the Ti44
abundance an observable diagnostic of supernovae. Through use of a nuclear
reaction network, we have systematically varied reaction rates and groups of
reaction rates to experimentally identify those that govern Ti44 abundance in
core-collapse supernova nucleosynthesis. We survey the nuclear-rate dependence
by repeated calculations of the identical adiabatic expansion, with peak
temperature and density chosen to be 5.5xE9 K and 1E7 g/cc, respectively, to
approximate the conditions in detailed supernova models. We find that, for
equal total numbers of neutrons and protons (eta=0), Ti44 production is most
sensitive to the following reaction rates: Ti44(alpha,p)V47,
alpha(2alpha,gamma)C12, Ti44(alpha,gamma)Cr48, V45(p,gamma)Cr46. We tabulate
the most sensitive reactions in order of their importance to the Ti44
production near the standard values of currently accepted cross-sections, at
both reduced reaction rate (0.01X) and at increased reaction rate (100X)
relative to their standard values. Although most reactions retain their
importance for eta > 0, that of V45(p,gamma)Cr46 drops rapidly for eta >=
0.0004. Other reactions assume greater significance at greater neutron excess:
C12(alpha,gamma)O16, Ca40(alpha,gamma)Ti44, Al27(alpha,n)P30, Si30(alpha,n)S33.
Because many of these rates are unknown experimentally, our results suggest the
most important targets for future cross section measurements governing the
value of this observable abundance.Comment: 37 pages, LaTex, 17 figures, 8 table
Studying the Evolution of Multi-Wavelength Emissivities with the Vimos VLT Deep Survey
The VIMOS VLT Deep Survey is a unique I-selected spectroscopic sample to
study galaxies all the way from z=5 to z=0. We recapitulate the first results
about the evolution of the galaxy populations as a function of type,
morphology, environment and luminosity.Comment: 9 pages, 11 figures. To appear in the proceedings of the XLIst
Rencontres de Moriond, XXVIth Astrophysics Moriond Meeting: "From dark halos
to light", Eds. L.Tresse, S. Maurogordato and J. Tran Thanh Van (Editions
Frontieres
Gamma ray constraints on the Galactic supernova rate
We perform Monte Carlo simulations of the expected gamma ray signatures of Galactic supernovae of all types to estimate the significance of the lack of a gamma ray signal due to supernovae occurring during the last millenium. Using recent estimates of the nuclear yields, we determine mean Galactic supernova rates consistent with the historic supernova record and the gamma ray limits. Another objective of these calculations of Galactic supernova histories is their application to surveys of diffuse Galactic gamma ray line emission
Gamma ray constraints on the galactic supernova rate
Monte Carlo simulations of the expected gamma-ray signatures of galactic supernovae of all types are performed in order to estimate the significance of the lack of a gamma-ray signal due to supernovae occurring during the last millenium. Using recent estimates of nuclear yields, we determine galactic supernova rates consistent with the historic supernova record and the gamma-ray limits. Another objective of these calculations of galactic supernova histories is their application to surveys of diffuse galactic gamma-ray line emission
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