High resolution infrared imaging and spectroscopy of the Pistol Nebula: evidence for ejection

We present new infrared images, obtained with the Hubble Space Telescope (HST) Near-infrared Camera and Multi-object Spectrometer (NICMOS), and Br-α (4.05 μm) spectroscopy, obtained using CGS4 on UKIRT, of the Pistol Star and its associated nebula. We find strong evidence to support the hypothesis that the Pistol Nebula was ejected from the Pistol Star. The Pa-α (1.87 μm) 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-α CGS4 spectra show the classical ring-like signature of quasi-spherical expansion. The blueshifted emission (Vmax ≈ −60 km s ) is much weaker than the redshifted emission (Vmax ≈ +10 km s ), where the velocities are with respect to the velocity of the Pistol Star; further, the redshifted emission spans a very narrow range of velocities, i.e., it appears “flattened” in the Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract No. NAS5-26555. Division of Astronomy, Department of Physics & Astronomy, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1562; [email protected], [email protected], [email protected], [email protected] Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 Gemini Observatory, 670 N. A’ohoku Place, Hilo, HI 96720; [email protected] JPL 171-113, 4800 Oak Grove Dr., Pasadena, CA 91109; [email protected] Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0111; [email protected] Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, NY 11794-3800; [email protected] Institut d’Astrophysique de Paris, 98 bis Blvd Arago, 75014 Paris, France