Is the magnetic field of a white-dwarf merely residual?

Question

Follow-up to my other question How does Sol's magnetic field continue to exist at such high temperatures?

Assuming Sol's magnetic field is generated by convective currents in it's plasma, how is it that the magnetic field still exists when the star ages to become a white-dwarf? Is the magnetic field of a white-dwarf merely residual?

Answer 1

I think that it was proposed that white dwarfs have magnetic fields because of conservation of total surface magnetic flux during the evolution of a non-degenerate star to a white dwarf.

It was thought initially that the so-called Blackett effect was the main cause of this magnetic field strength but observations have been sparse (actually, come to think of it, none at all). The Blackett effect is the generation of a magnetic field by an uncharged, rotating body.

Answer 2

White dwarf high magnetic field is now thought to be connected to a compagnion star (most of WD are binarie). A likely origin of the high magnetic fields is a magnetic dynamo operating during common envelope evolution. For solitary highly magnetic white dwarfs, the trend is to think the magnetic field has resulted from core merging in a common envelope.