Quantifying the uncertainties of chemical evolution studies. II. Stellar
  yields
  This is the second paper of a series which aims at quantifying the
uncertainties in chemical evolution model predictions related to the underlying
model assumptions. Specifically, it deals with the uncertainties due to the
choice of the stellar yields. We adopt a widely used model for the chemical
evolution of the Galaxy and test the effects of changing the stellar
nucleosynthesis prescriptions on the predicted evolution of several chemical
species. We find that, except for a handful of elements whose nucleosynthesis
in stars is well understood by now, large uncertainties still affect the model
predictions. This is especially true for the majority of the iron-peak
elements, but also for much more abundant species such as carbon and nitrogen.
The main causes of the mismatch we find among the outputs of different models
assuming different stellar yields and among model predictions and observations
are: (i) the adopted location of the mass cut in models of type II supernova
explosions; (ii) the adopted strength and extent of hot bottom burning in
models of asymptotic giant branch stars; (iii) the neglection of the effects of
rotation on the chemical composition of the stellar surfaces; (iv) the adopted
rates of mass loss and of (v) nuclear reactions, and (vi) the different
treatments of convection. Our results suggest that it is mandatory to include
processes such as hot bottom burning in intermediate-mass stars and rotation in
stars of all masses in accurate studies of stellar evolution and
nucleosynthesis. In spite of their importance, both these processes still have
to be better understood and characterized. As for massive stars, presupernova
models computed with mass loss and rotation are available in the literature,
but they still wait for a self-consistent coupling with the results of
explosive nucleosynthesis computations.
