Measuring the Local ISM along the Sight Lines of the Two Voyager
  Spacecraft with HST/STIS
  In 2012, Voyager 1 crossed the heliopause, becoming the first human-made
object to exit the solar system. This milestone signifies the beginning of an
important new era for local interstellar medium (LISM) exploration. We present
measurements of the structure and composition of the LISM in the immediate path
of the Voyager spacecraft by using high-resolution Hubble Space Telescope (HST)
spectra of nearby stars that lie along the same lines of sight. We provide a
comprehensive inventory of LISM absorption in the near-ultraviolet (2600-2800
Angstroms) and far-ultraviolet (1200-1500 Angstroms). The LISM absorption
profiles are used to make comparisons between each pair of closely spaced (<15
deg) sight lines. With fits to several absorption lines, we make measurements
of the physical properties of the LISM. We estimate electron density along the
Voyager 2 sight line, and our values are consistent with recent measurements by
Voyager 1. Excess absorption in the HI Ly-alpha line displays the presence of
both the heliosphere and an astrosphere around GJ 780. This is only the 14th
detection of an astrosphere, and the large mass-loss rate ($\dot{M} =
10\dot{M}_\odot$) is consistent with other subgiant stars. The heliospheric
absorption matches the predicted strength for a sight line 58 deg from the
upwind direction. As both HST and Voyager reach the end of their lifetimes, we
have the opportunity to synthesize their respective observations, combining in
situ measurements with the shortest possible line-of-sight measurements to
study the Galactic ISM surrounding the Sun.
