Could interstellar metals be more from stellar winds than from supernovae?

As far as we know, heavy elements only form in the core of stars. Elements heavier than iron (up to and including bismuth) are created in a star's core by neutron capture. Heavier elements (up to and including uranium) are created in the energy flux of supernovae.

There may be other esoteric processes in the Universe which contribute a tiny bit to the pool of heavy elements, but it would be negligible in comparison to the primary source (exploding stars).

Yes, but convection brings some of the metals from core to surface eventually. (If it didn't, we'd never see their lines in a stellar spectrum.) Might such convection increase enough in the red giant phase to bring significantly more metals to the surface and then stellar winds?

I don't know. Where did you hear this theory?

Star cores are highly stratified and very stable due to the intense gravitational field. I'm not sure much if anything gets to the surface by convection.

Also I'm not sure elements need to be brought to the surface in order for them to effect the spectrum of the starlight. I think the material from the core produces photons which eventually (after a LONG time) make it out to the photosphere. But I'm not entirely certain about that.

Do you have any links you can reference on this?

That is an interesting question. I would guess we really don’t know the definitive answer to that as our understanding of stellar interiors and the exact metalicity of the various types of stars is still incomplete. It is certainly possible. Off the top of my head I know that models over a couple of decades predicted consistently at least 1/3 of all gas (matter) returned to our galaxy comes from spectral A type stars. The great majority of the other 2/3 comes from red supergiants and planetary nebula. ALL other sources (including supernovas) make up probably no more that 5% total. Really it is probably less.

So the only significant consideration is the amount of metals that these three sources emit. Since normal pop II stars can be as much as 5% metal by mass it again seems plausible.

You can start by looking up Barium stars, Technetium stars, and Molybdenum stars. You are very wrong about most stars being stratified; this is not as common as you seem to state. In fact some sectrum variables are such because the composition at the poles is so different than that of other areas of the stars. In some type stars convection goes from surface to core, in fact these stars have convective rather than radiative cores for the most part.

You might also want to bone up on stellar photons. A photon that starts in the stellar interior NEVER makes it to the surface. In fact in the radiative core a photon mean free path is less than the diameter of a hydrogen atom -- in other words they never enter free space but are passed on from one atom to the next. Quantum theory charges us to call each photon after an interaction a new photon. Besides for your point to be valid you would actually seem to be arguing for the photon “remembering” its history and where it came from.