  Recently published Spitzer observations of the classical Cepheid archetype
delta Cephei revealed an extended dusty nebula surrounding this star and its
hot companion. The infrared emission resembles a bow shock aligned with the
direction of space motion of the star, indicating that delta Cep is undergoing
mass-loss through a stellar wind. Here we report HI 21-cm line observations
with the VLA to search for neutral atomic hydrogen associated with this wind.
Our VLA data reveal a spatially extended HI nebula (~13' or 1 pc across)
surrounding the position of delta Cep. The nebula has a head-tail morphology,
consistent with circumstellar ejecta shaped by the interaction between a
stellar wind and the ISM. We directly measure a mass of circumstellar hydrogen
M_HI\approx0.07M_odot, although the total HI mass may be larger. The HI data
imply a stellar wind with an outflow velocity V_o=35.6\pm1.2 km/s and a
mass-loss rate of M_dot=(1.0\pm0.8)x10**-6 M_dot/yr. We have computed
theoretical evolutionary tracks that include mass loss across the instability
strip and show that a mass-loss rate of this magnitude, sustained over the
preceding Cepheid lifetime of delta Cep, could be sufficient to resolve a
significant fraction of the discrepancy between the pulsation and evolutionary
masses for this star. (abridged)
