3,186 research outputs found
Uncertainties in AGB Evolution and Nucleosynthesis
We summarise the evolution and nucleosynthesis in AGB and Super-AGB stars. We
then examine the major sources of uncertainty, especially mass-loss.Comment: 8 pages, no figures. Invited review presented at The 11th Pacific Rim
Conference on Stellar Astrophysics "Physics and Chemistry of the Late Stages
of Stellar Evolution
Relative entropy methods for hyperbolic and diffusive limits
We review the relative entropy method in the context of hyperbolic and diffusive relaxation limits of
entropy solutions for various hyperbolic models. The main example consists of the convergence from
multidimensional compressible Euler equations with friction to the porous medium equation \cite{LT12}.
With small modifications, the arguments used in that case can be adapted to the study of the
diffusive limit from the Euler-Poisson system with friction to the Keller-Segel system \cite{LT13}.
In addition, the --system with friction and the system of viscoelasticity with memory are then reviewed,
again in the case of diffusive limits \cite{LT12}.
Finally, the method of relative entropy is described for the multidimensional stress relaxation model converging to elastodynamics \cite[Section 3.2]{LT06}, one of the first examples of application of the method to hyperbolic relaxation limits
Structure, Evolution and Nucleosynthesis of Primordial Stars
(abridge version) The evolution of population III stars (Z=0) is followed
from the pre-main sequence phase up to the AGB phase for intermediate-mass
stars and up to C ignition in more massive stars...We find that, thanks to the
development of mixing episodes (carbon injections) at the beginning of the AGB
phase, the carbon abundance of the 1, 1.5, 2, 3, 4 and 5Mo models is
significantly increased in the envelope. This process then allows low- and
intermediate-mass stars to achieve a ``standard'' thermally pulsing AGB
phase... In the 7Mo model, the CNO envelope abundance following the second
dredge-up is so large that the star does not experience the carbon injection
episode and follows a more standard thermally pulsing AGB evolution. Our
computations also indicate that, thanks to a small overshooting at the base of
the convective envelope, the third dredge-up is already operating in stars with
M >~1.5 Mo after a few pulses, and that by the end of our modeling, hot bottom
burning is activated in stars more massive than ~ 2Mo. This evolutionary
behavior suggests that primordial low- and intermediate stars could have been
significant contributors to the production of primary 12C, 14N, and may have
contributed to some extent to the production of Mg and Al and possibly
s-elements (despite the lack of iron seeds) in the early universe.Comment: 26 pages, 13 figures, 6 tables, uses aastex. Accepted for publication
in ApJ. Full postscript version available at
http://www-astro.ulb.ac.be/~sies
Nucleosynthesis of Elements in Low to Intermediate Mass Stars through the AGB Phase
We present a review of the main phases of stellar evolution with particular
emphasis on the nucleosynthesis and mixing mechanisms in low- and
intermediate-mass stars. In addition to explicit studies of the effects of the
first, second and third dredge-up, we also discuss cool bottom processing and
hot bottom burning.Comment: 30 pages, latex, 18 figures, uses style files aipproc.cls aipproc.sty
epsf.sty ; to be published in (refereed) conference proceedings
"Astrophysical Implications of the Laboratory Study of Presolar Materials",
ed. T. Bernatowitz and E. Zinner (AIP: Sunnyside, NY), in press; also
available at http://www.maths.monash.edu.au/~boothroy
Shock waves for radiative hyperbolic--elliptic systems
The present paper deals with the following hyperbolic--elliptic coupled
system, modelling dynamics of a gas in presence of radiation, where , and
, , . The flux function is smooth and
such that has distinct real eigenvalues for any . The problem
of existence of admissible radiative shock wave is considered, i.e. existence
of a solution of the form , such that
, and , define a shock wave
for the reduced hyperbolic system, obtained by formally putting L=0. It is
proved that, if is such that ,(where denotes the -th eigenvalue of and a
corresponding right eigenvector) and , then there exists a neighborhood of such
that for any , such that the triple
defines a shock wave for the reduced hyperbolic system, there
exists a (unique up to shift) admissible radiative shock wave for the complete
hyperbolic--elliptic system. Additionally, we are able to prove that the
profile gains smoothness when the size of the shock is
small enough, as previously proved for the Burgers' flux case. Finally, the
general case of nonconvex fluxes is also treated, showing similar results of
existence and regularity for the profiles.Comment: 32 page
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