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Recent improvements in stellar models for intermediate-mass and massive stars are recalled, together with their expectations for the synthesis of radioactive nuclei of lifetime $\tau \lesssim 25$ Myr, in order to re-examine the origins of now extinct radioactivities, which were alive in the solar nebula. The Galactic inheritance broadly explains most of them, especially if $r$-process nuclei are produced by neutron star merging according to recent models. Instead, $^{26}$Al, $^{41}$Ca, $^{135}$Cs and possibly $^{60}$Fe require nucleosynthesis events close to the solar formation. We outline the persisting difficulties to account for these nuclei by Intermediate Mass Stars (2 $\lesssim $ M/M$_\odot \lesssim 7 - 8$). Models of their final stages now predict the ubiquitous formation of a $^{13}$C reservoir as a neutron capture source; hence, even in presence of $^{26}$Al production from Deep Mixing or Hot Bottom Burning, the ratio $^{26}$Al/$^{107}$Pd remains incompatible with measured data, with a large excess in $^{107}$Pd. This is shown for two recent approaches to Deep Mixing. Even a late contamination by a Massive Star meets problems. In fact, inhomogeneous addition of Supernova debris predicts non-measured excesses on stable isotopes. Revisions invoking specific low-mass supernovae and/or the sequential contamination of the pre-solar molecular cloud might be affected by similar problems, although our conclusions here are weakened by our schematic approach to the addition of SN ejecta. The limited parameter space remaining to be explored for solving this puzzle is discussed., Comment: Accepted for publication on ApJ

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New stellar models with masses ranging between 4 and 8 Msolar, Z=0, and Y=0.23 are presented. The models have been evolved from the pre-main sequence up to the asymptotic giant branch (AGB). At variance with previous claims, we find that these updated stellar models do experience thermal pulses in the AGB phase. In particular, we show the following:1. In models with a mass larger than 6 Msolar, the second dredge-up is able to raise the CNO abundance in the envelope enough to allow a normal AGB evolution, in the sense that the thermal pulses and the third dredge-up take place. 2. In models of lower mass, the efficiency of the CNO cycle in the H-burning shell is controlled by the carbon produced locally via the 3a reactions. Nevertheless, the He-burning shell becomes thermally unstable after the early AGB. The expansion of the overlying layers induced by these weak He-shell flashes is not sufficient by itself to allow a deep penetration of the convective envelope. However, soon after the development of the maximum luminosity of the He flash is attained, a convective shell systematically forms at the base of the H-rich envelope. The innermost part of this convective shell probably overlaps the underlying C-rich region left by the intershell convection during the thermal pulse so that fresh carbon is dredged up in a hot H-rich environment and an H flash occurs. This flash favors the expansion of the outermost layers already started by the weak thermal pulse, and a deeper penetration of the convective envelope takes place. Then the carbon abundance in the envelope rises to a level high enough that the further evolution of these models closely resembles that of more metal-rich AGB stars. These stars provide an important source of primary carbon and nitrogen, so a major revision of the chemical evolution in the early Galaxy is required. We suggest that the chemical imprint of these Population III stars could be found in the old and metal-poor components of the Milky Way.

We present a theoretical model for Type Ib supernova (SN) 2006jc. We calculate the evolution of the progenitor star, hydrodynamics and nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC). The synthetic bolometric LC is compared with the observed bolometric LC constructed by integrating the UV, optical, near-infrared (NIR), and mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as $40M_\odot$ on the zero-age main-sequence. The star undergoes extensive mass loss to reduce its mass down to as small as $6.9M_\odot$, thus becoming a WCO Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which amorphous carbon grains can be formed. This could explain the NIR brightening and the dust feature seen in the MIR spectrum. We suggest that the progenitor of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and such massive stars are the important sites of dust formation. We derive the parameters of the explosion model in order to reproduce the bolometric LC of SN 2006jc by the radioactive decays: the ejecta mass $4.9M_\odot$, hypernova-like explosion energy $10^{52}$ ergs, and ejected $^{56}$Ni mass $0.22M_\odot$. We also calculate the circumstellar interaction and find that a CSM with a flat density structure is required to reproduce the X-ray LC of SN 2006jc. This suggests a drastic change of the mass-loss rate and/or the wind velocity that is consistent with the past luminous blue variable (LBV)-like event., Comment: 12 pages, 11 figures. Accepted for publication in the Astrophysical Journal

We discuss the production sites of the nuclei from C to Al in solar metallicity stars in the range $\rm 13-35~M_\odot$. We will show how, contrarily to corrent believings, the advanced burning phases and the passage of the blast wave play a pivotal role in determing the final yields of quite a few "light" nuclei. We will also show how the relative contributions of the hydrostatic and explosive burnings depend on the initial mass of the star: the smaller the mass the larger the importance of the explosive burnings.

We present a set of models of AGB stars with initial mass larger than 5 Mo as obtained with the FRANEC code. It includes models of Z=0.02 and Z=0.001, with and without mass loss., Comment: 9 pages, 9 figures (memsait.sty, epsf.sty) contribution to the workshop "The Changes in Abundances in Asymptotic Giant Branch Stars", held in Monte Porzio Catone (Italy), September 1999, to be published by Mem.Soc.Astron.It., eds. F. D'Antona and R. Gallino