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 τ≲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, 26Al, 41Ca, 135Cs and possibly 60Fe require
nucleosynthesis events close to the solar formation. We outline the persisting
difficulties to account for these nuclei by Intermediate Mass Stars (2
≲ M/M⊙≲7−8). Models of their final stages now
predict the ubiquitous formation of a 13C reservoir as a neutron capture
source; hence, even in presence of 26Al production from Deep Mixing or Hot
Bottom Burning, the ratio 26Al/107Pd remains incompatible with
measured data, with a large excess in 107Pd. 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 Ap