Df. Figer et al., High-resolution infrared imaging and spectroscopy of the Pistol nebula: Evidence for ejection, ASTROPHYS J, 525(2), 1999, pp. 759-771
We present new infrared images, obtained with the Hubble Space Telescope (H
ST) Near-Infrared Camera and Multiobject Spectrometer (NICMOS), and Br alph
a (4.05 mu m) spectroscopy, obtained using CGS4 on UKIRT, of the Pistol Sta
r and its associated nebula. We find strong evidence to support the hypothe
sis that the Pistol Nebula was ejected from the Pistol Star. The Pa alpha (
1.87 mu m) NICMOS image shows that the nebula completely surrounds the Pist
ol Star, although the line intensity is much stronger on its northern and w
estern edges. The Br alpha CGS4 spectra show the classical ringlike signatu
re of quasi-spherical expansion. The blueshifted emission (V-max approximat
e to -60 km s(-1)) is much weaker than the redshifted emission (V-max appro
ximate to + 10 km s(-1)), where the velocities are with respect to the velo
city of the Pistol Star; further, the redshifted emission spans a very narr
ow range of velocities, i.e., it appears "flattened" in the position-veloci
ty diagram. These data suggest that the nebula was ejected from the star se
veral thousand years ago, with a velocity between the current terminal velo
city of the stellar wind (95 km s(-1)) and the present expansion velocity o
f gas in the outer shell of the nebula (60 km s(-1)). The Pa alpha image re
veals several emission-line stars in the region, including two newly identi
fied emission-line stars north of the Pistol Star, both of which are likely
to be the hottest known stars in the Galactic center with spectral types e
arlier than WC8 and T-eff > 50,000 K). The presence of these stars, the mor
phology of the Pa alpha emission, and the velocity held in the gas suggest
that the side of the nebula farthest from us is approaching, and being ioni
zed by, the hot stars of the Quintuplet and that the highest velocity redsh
ifted 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 held delineated by the nearby nonthermal filaments
.