Silicate Mineralogy of the Dust in the Inner Coma of Comet C/1995 01 (Hale‐Bopp) Pre‐ and Postperihelion

• DOI: 10.1086/307206
• Publication Date: 2002-07-26T18:53:12Z
• Authors: Diane H. Wooden; David E. Harker; Charles E. Woodward; Harold M. Butner; Chiyoe Koike; Fred C. Witteborn; Craig W. McMurtry
• Keywords: Pyroxene

We present 7.5-13.4 μm infrared (IR) spectrophotometry (R≃180-360) of the 10 silicate emission from dust in inner coma (i.e., within a diameter 3'') comet C/1995 O1 (Hale-Bopp) at four temporal epochs 1996 October through 1997 June during Hale-Bopp's approach to, arrival at, and recession perihelion. feature is strongest observed any to date: flux-to-continuum ratio 10.0 2.5 2.8 AU preperihelion, increases 3.0 0.93 AU, then decreases 2.4 1.7 postperihelion, dropping more rapidly strength than expected preperihelion spectra indicating diminishment relative abundance submicron sized grains by perihelion passage. The also evolves with heliocentric distance. When far perihelion, ~2.8 High Efficiency Faint Object Grating Spectrometer (HIFOGS) contains 9.3 shoulder attributable amorphous pyroxene, broad olivine (9.7 μm), 11.2 peak associated crystalline olivine. Concurrent HIFOGS Infrared Space Observatory (ISO) Short Wavelength (SWS) spectrum shows strong far-IR peaks 18 μm, 23 33 μm. close include newly discovered peak, identifiable as Mg-rich pyroxene. hypothesize that pyroxenes are cooler other silicates, too cool be detected but warm enough 1.2 AU. best-fit empirical model for evolution constrains dominated ortho-pyroxene rather clino-pyroxene. have color temperature 0.6 times an about 9 greater silicates all epochs, assuming equivalent particle size distributions components. Comparing radiative equilibrium, both Mg number 0.9, crystals because they less absorbing visible near-IR wavelengths. Thus, it high content accounts their temperature. dominance among cometary consistent PUMA-1 mass spectrometer measurements P/Halley 1986 III interplanetary particles. Hale-Bopp implies either pristine solar nebula condensates or presolar such recently ISO around asymptotic giant branch stars.