  We present new NICMOS/HST infrared images and CGS4/UKIRT Br-alpha (4.05 um)
spectroscopy of the Pistol Star and its associated nebula, finding strong
evidence to support the hypothesis that the Pistol Nebula was ejected from the
Pistol Star. The Pa-alpha NICMOS image shows that the nebula completely
surrounds the Pistol Star, although the line intensity is much stronger on its
northern and western edges. The Br-alpha spectra show the classical ring-like
signature of quasi-spherical expansion, with weak blueshifted emission (V_max
approx -60 km/s) and strong redshifted emission (V_max approx +10 km/s), where
the velocities are with respect to the velocity of the Pistol Star; further,
the redshifted emission appears to be "flattened" in the position-velocity
diagram. These data suggest that the nebula was ejected from the star several
thousand years ago, with a velocity between the current terminal velocity of
the stellar wind (95 km/s) and the present expansion velocity of gas in the
outer shell of the nebula (60 km/s). The Pa-alpha image reveals several
emission-line stars in the region, including two newly-identified emission-line
stars north of the Pistol Star with spectral types earlier than WC8 (T_eff >
50,000 K). The presence of these stars, the morphology of the Pa-alpha
emission, and the velocity field in the gas suggest that the side of the nebula
furthest from us is approaching, and being ionized by, the hot stars of the
Quintuplet, and that the highest velocity redshifted gas has been decelerated
by winds from the Quintuplet stars. We also discuss the possibility that the
nebular gas might be magnetically confined by the ambient magnetic field
delineated by the nearby nonthermal filaments.
