### B.1 Spin-orbit coupling force

It is well known that the definition of a dipole moment of the star, which we equate to zero to determine
the center of mass of the star, affects the appearance of the spin-orbit coupling force (see e.g. [108]). If one
chooses as in [94], the corresponding spin-orbit coupling force takes the usual form [46, 108, 152]
where and in this section denotes the outer product for the usual Euclidean
spatial three-vectors. The spin vector is defined by
where is the totally antisymmetric symbol.