RESUMO
Spitzer Space Telescope imaging spectrometer observations of comet 9P/Tempel 1 during the Deep Impact encounter returned detailed, highly structured, 5- to 35-micrometer spectra of the ejecta. Emission signatures due to amorphous and crystalline silicates, amorphous carbon, carbonates, phyllosilicates, polycyclic aromatic hydrocarbons, water gas and ice, and sulfides were found. Good agreement is seen between the ejecta spectra and the material emitted from comet C/1995 O1 (Hale-Bopp) and the circumstellar material around the young stellar object HD100546. The atomic abundance of the observed material is consistent with solar and C1 chondritic abundances, and the dust-to-gas ratio was determined to be greater than or equal to 1.3. The presence of the observed mix of materials requires efficient methods of annealing amorphous silicates and mixing of high- and low-temperature phases over large distances in the early protosolar nebula.
RESUMO
Near-infrared spectra with a resolution of lambda&solm0;Deltalambda approximately 1100 in the rest-wavelength range of 1.8-2.2 µm have been obtained for a complete sample of 33 ultraluminous infrared galaxies (ULIRGs). Of the 33 objects observed, two show evidence of a central active galactic nucleus (AGN) through either a broad Paschen-alpha line or emission in the 1.963 µm fine structure of [Si vi]. In the median spectrum of the remaining 31 objects, the lines present are recombination lines of hydrogen and neutral helium, vibration-rotation lines of H2, and [Fe ii]. There is no indication of AGN activity in the median spectrum, either through broad atomic recombination lines or through high ionization lines. No trends in luminosity are apparent when subsets of the 31 non-AGN ULIRGs are binned by luminosity and median-combined. When secondary nuclei exist in ULIRGs, they typically have spectra very much like those seen in the primary nuclei.
