Interstellar HI Shells Identified in the SETHI Survey
  Galactic HI (neutral hydrogen) shells are central to our understanding of the
interstellar medium (ISM), which plays a key role in the development and
evolution of galaxies, including our own. Several models involving supernovae
and stellar winds have contributed to our broad understanding, but a complete,
detailed picture remains elusive. To extend existing Galactic shell catalogs,
we visually examined the SETHI (Search for Extraterrestrial HI) database to
identify shell-like structures. This high-sensitivity 21-cm radio survey
covering the Arecibo sky uniquely provides high-resolution data on shells at a
wide range of Galactic latitudes. We present basic information (location,
radial velocity, angular size, shape) for 74 previously unidentified HI shells.
Due to limitations of coverage and data quality, and the biases inherent in
search techniques, our catalog is not a complete sample of Galactic shells. We
discuss the catalog completeness, and comment on the new shells' relationship
with known interstellar structure as warranted. Unlike many previous catalogs,
this sample is not biased towards expanding shells. Where possible we also
estimate the kinematic distances, physical sizes, expansion velocities, and
energies of these shells. Overall, they are relatively large and old, each the
result of multiple supernovae. Unlike previous surveys, we do not find that the
shells in our sample are preferentially aligned relative to the Galactic plane.
