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L.F. Lim, J.F. Bell, B.E. Clark, T.H. McConnochie (Cornell University), T.L. Hayward (Gemini Observatory), A. Barucci (Obs. Paris), E. Dotto (Obs. Turin)
Silicate minerals, which form the major constituents of asteroid surfaces, exhibit important diagnostic emissivity features in the thermal infrared. Some of these minerals, such as plagioclase and coarse-grained iron oxides, cannot be detected unambiguously using visible to near-IR spectroscopy. Mid-IR spectra, therefore, may provide additional diagnostic information that is needed to resolve ambiguities in the current asteroid classification scheme, which is based on visible to near-IR measurements. Published spectra by Dotto et al. (A & A 358,2000) of the small number of asteroids studied by ISO appear to validate this claim.
We report the initial results of the Cornell Mid-IR Asteroid Spectroscopy (MIDAS) survey. MIDAS covers the 8-14 micron wavelength region and is conducted at Palomar Observatory using the Spectrocam-10 (SC-10) spectrograph on the 200-inch Hale telescope. We have conducted two short observing runs to date, on 09 October 2000 and 09 April 2001 and have obtained mid-IR spectra of the S-type asteroid 3 Juno and the C-type asteroid 145 Adeona. Although these spectra were obtained under non-photometric conditions, they validate our estimates of the signal to noise ratios that could be expected from a variety of main belt and near-Earth objects using SC-10. Further observations are planned for October 1-2, 2001. Targets include 4 Vesta (V-class), 11 Parthenope (S-class), 22 Kalliope (M-class), 54 Arethusa (C-class) and others. We hope to sample the spectra of a statistically significant number of asteroids from a wide variety of the current visible to near-IR spectral classes.