608 research outputs found
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
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
Molecular opacities for low-mass metal-poor AGB stars undergoing the Third Dredge Up
The concomitant overabundances of C, N and s-process elements are commonly
ascribed to the complex interplay of nucleosynthesis, mixing and mass loss
taking place in Asymptotic Giant Branch stars. At low metallicity, the
enhancement of C and/or N may be up to 1000 times larger than the original iron
content and significantly affects the stellar structure and its evolution. For
this reason, the interpretation of the already available and still growing
amount of data concerning C-rich metal-poor stars belonging to our Galaxy as
well as to dwarf spheroidal galaxies would require reliable AGB stellar models
for low and very low metallicities. In this paper we address the question of
calculation and use of appropriate opacity coefficients, which take into
account the C enhancement caused by the third dredge up. A possible N
enhancement, caused by the cool bottom process or by the engulfment of protons
into the convective zone generated by a thermal pulse and the subsequent huge
third dredge up, is also considered. Basing on up-to-date stellar models, we
illustrate the changes induced by the use of these opacity on the physical and
chemical properties expected for these stars.Comment: 23 pages, 8 figures, accepted for publication in Ap
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