Mid-infrared observation of the dust plume from comet 9P/tempel 1 generated by the Deep Impact collision using Subaru/comics

We carried out mid-infrared observations (multi-band imaging and N-band spectroscopy) of the Deep Impact collision with a Jupiter family comet 9P/Tempel 1 using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the 8.2 m Subaru Telescope. Imaging observations reveal that a large fan-shaped impact ejecta was extended to the south-west direction from the nucleus, which is close to the surface normal vector of the impact point of the comet. The N-band spectrum (8-13 μm; R ∼ 250) of the dust ejecta from the comet nucleus 3.5 hours after the Deep Impact event shows a strong crystalline olivine feature. We also made spectroscopic observations 24 hours before and 28 hours after the impact. These spectra have no evident silicate feature in the 10 μm region. We present several spectra at the different positions from the comet nucleus, and report the preliminary result of our fitting analysis using a thermal emission model of cometary dust grains. The mass ratio of crystalline to amorphous silicate grains for the dust ejected from the subsurface of 9P/Tempel 1 is much larger than the dust in the coma of other Jupiter family comet, such as 78P/Gehrels 2, but similar to Oort cloud comets, such as Hale-Bopp.