  As the local interstellar plasma flows past our heliosphere, it is slowed and
deflected around the magnetic obstacle of the heliopause. The interstellar
magnetic field, frozen into this plasma, then becomes draped around the
heliopause in a characteristic manner. We derive the analytical solution for
this draped magnetic field in the limit of weak field intensity, assuming an
ideal potential flow around the heliopause, which we model as a Rankine
half-body. We compare the structure of the model magnetic field with observed
properties of the IBEX ribbon and with in situ observations at the Voyager 1
spacecraft. We find reasonable qualitative agreement, given the idealizations
of the model. This agreement lends support to the secondary ENA model of the
IBEX ribbon and to the interpretation that Voyager 1 has crossed the
heliopause. We also predict that the magnetic field measured by Voyager 2 after
it crosses the heliopause will not be significantly rotated away from the
direction of the undisturbed interstellar field.
