  Consider a planet with its orbital angular momentum axis aligned with the
spin axis of its host star. To what extent does an inclined distant companion
(giant planet or binary star) affect this alignment? We provide an analytic,
quantitative answer and apply it to hot Jupiter systems, for which
misalignments between the orbital axis and the stellar spin axis have been
detected. We also show how similar consideration can be applied to multi-planet
systems with distant companions (such as Kepler-56). The result of this paper
provides a simple method to assess the dynamical role played by external
companions on spin-orbit misalignments in exoplanetary systems.
