Fractional yields inferred from halo and thick disk stars
  Linear [Q/H]-[O/H] relations, Q = Na, Mg, Si, Ca, Ti, Cr, Fe, Ni, are
inferred from a sample (N=67) of recently studied FGK-type dwarf stars in the
solar neighbourhood including different populations. Regression line slope and
intercept estimators and related variance estimators are determined. With
regard to the straight line, [Q/H] = aQ [O/H] + bQ, sample stars display along
a "main sequence", [Q,O] = [aQ,bQ, Delta bQ], leaving aside the two OL stars
which, in most cases (e.g., Na), lie outside. A unit slope, aQ = 1, implies Q
is a primary element synthesised via SNII progenitors in presence of universal
stellar initial mass function (defined as simple primary element). To this
respect, Mg, Si, Ti, show aQ = 1 within 2 sigma(aQ); Cr, Fe, Ni, within 3
sigma(aQ); Na, Ca, exceeding 3 sigma(aQ). The empirical, differential element
abundance distributions are inferred from different subsamples, where related
regression lines represent their theoretical counterparts within the framework
of simple MCBR (multistage closed box + reservoir) chemical evolution models.
Hence the fractional yields are determined and (as an example) a comparison is
shown with their theoretical counterparts inferred from SNII progenitor
nucleosynthesis under the assumption of a power-law stellar initial mass
function. The generalized fractional yields are determined regardless from the
chemical evolution model. The ratio of outflow to star formation rate is
compared for different populations, in the framework of simple MCBR models. The
opposite situation of element abundance variation entirely due to cosmic
scatter is also considered under reasonable assumptions. The related
differential element abundance distribution fits to the data as well as its
counterpart inferred in the opposite limit of instantaneous mixing in presence
of chemical evolution.
