  Ultraviolet spectra from the GHRS instrument on board the Hubble Space
Telescope reveal the presence of a mysterious absorption feature in the Mg II h
& k lines of the nearby (d=20.0 pc) K5 III star Alpha Tau. The narrow
absorption looks like an interstellar absorption feature but it is in the wrong
location based on our knowledge of the local ISM flow vector. Since the
absorption is close to the rest frame of the star, it has been interpreted as
being from the interaction region between Alpha Tau's massive, cool wind and
the interstellar medium, i.e., Alpha Tau's "astrosphere". We compute
hydrodynamic models of the Alpha Tau astrosphere in order to see if the models
can reproduce the Mg II absorption feature. These models do predict that
stellar wind material heated, decelerated, and compressed after passing through
a termination shock a few thousand AU from the star should produce a Mg II
absorption feature with about the right width at roughly the right velocity.
However, our first models underestimate the Mg II column density by an order of
magnitude. A much larger parameter search is necessary to see whether the
observed Mg II absorption can be reproduced by acceptable changes to the
adopted stellar wind and ISM properties.
