563 research outputs found
Evolution, nucleosynthesis and yields of AGB stars at different metallicities (III): intermediate mass models, revised low mass models and the ph-FRUITY interface
We present a new set of models for intermediate mass AGB stars (4.0, 5.0 and,
6.0 Msun) at different metallicities (-2.15<=Fe/H]<=+0.15). This integrates the
existing set of models for low mass AGB stars (1.3<=M/M<=3.0) already included
in the FRUITY database. We describe the physical and chemical evolution of the
computed models from the Main Sequence up to the end of the AGB phase. Due to
less efficient third dredge up episodes, models with large core masses show
modest surface enhancements. The latter is due to the fact that the interpulse
phases are short and, then, Thermal Pulses are weak. Moreover, the high
temperature at the base of the convective envelope prevents it to deeply
penetrate the radiative underlying layers. Depending on the initial stellar
mass, the heavy elements nucleosynthesis is dominated by different neutron
sources. In particular, the s-process distributions of the more massive models
are dominated by the \nean~reaction, which is efficiently activated during
Thermal Pulses. At low metallicities, our models undergo hot bottom burning and
hot third dredge up. We compare our theoretical final core masses to available
white dwarf observations. Moreover, we quantify the weight that intermediate
mass models have on the carbon stars luminosity function. Finally, we present
the upgrade of the FRUITY web interface, now also including the physical
quantities of the TP-AGB phase of all the models included in the database
(ph-FRUITY).Comment: Accepted for publication on ApJ
On the mass of supernova progenitors: the role of the CC reaction
A precise knowledge of the masses of supernova progenitors is essential to
answer various questions of modern astrophysics, such as those related to the
dynamical and chemical evolution of Galaxies. In this paper we revise the upper
bound for the mass of the progenitors of CO white dwarfs (\mup) and the lower
bound for the mass of the progenitors of normal type II supernovae (\mups). In
particular, we present new stellar models with mass between 7 and 10 \msun,
discussing their final destiny and the impact of recent improvements in our
understanding of the low energy rate of the \c12c12 reaction.Comment: To be published on the proceedings of NIC 201
Outer core density heterogeneity and the discrepancy between PKP and PcP travel time observations
We derive 3-D maps of the Earth’s mantle, CMB and outer
core by means of least squares tomographic inversions. The data set includes
compressional wave travel time measurements associated with the phases P,
PcP, PKPbc, PKPdf, all based on the bulletins of the International Seismological
Centre (1964-1995), after source relocation by Antolik et al. [2001].
Maps of the CMB derived independently from only core-reflected (PcP) or
only core-refracted (PKP) phases are not well correlated. We study the radial
coherence of whole-Earth tomographic images, to investigate potential
trade-offs between CMB undulations and velocity anomalies in the mantle
and/or outer core. We find that imaged lateral heterogeneities in the outer
core are correlated with the topography of the CMB. This, together with the
studies of Wahr and De Vries [1989] and Piersanti et al. [2001], suggests that
the core anomalies might not be entirely fictitious
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