  We consider the D7/D(--1) system in Type I' as a prototypical "exotic" brane
instanton. With respect to systems such as the D3/D(-1) ones, which correspond
to gauge instantons in four dimensions, exotic systems lack the bosonic mixed
moduli w of the ADHM construction, related to the instanton size, and their
possible field-theoretical interpretation as classical solutions is an
important open question. For the system at hand, we propose that it corresponds
to the point-like limit of the eight-dimensional so-called SO(8) instanton
solution. This configuration is a solution of the quartic term of the
non-abelian D7 action, i.e., the term which stays finite in the limit in which
alpha' goes to zero with the string coupling fixed that preserves the D(-1)
effects. As a necessary consistency condition, we check that the next order
term in the non-abelian effective action vanishes on the SO(8) solution so that
the limit we take is well-defined.
