0.4-3.5-micrometer Observations of 4179 Toutatis


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Asteroids, Apollo, Pyroxenes, Spectral Reflectance

Scientific paper

We obtained nearly simultaneous observations of 4179 Toutatis over a 0.3-3.5 micrometer wavelength range on 4 January 1993 UT. Howell obtained a 1.2-2.5 micrometer spectrophotometry using the Multiple Mirror Telescope in Arizona. Britt and Bell obtained narrowband photometry in the 3-micrometer region as well as broadband JHK photometry from the Infrared Telescope Facility in Hawaii. Binzel measured the visible spectrum using a CCD spectrograph at the McGraw-Hill Observatory in Arizona. Using V photometry reported by Pravec in the Czech Republic on adjacent nights [1], we were able to combine all these spectral regions. The rotation period of this object is approximately 10 days, so the time differences between the measurements of different spectral regions are negligible. Tholen has classified 4179 Toutatis as an S-type asteroid based on visible photometry. We measure a pyroxene absorption band near 2 micrometers, present in most S-type asteroid spectra. Unfortunately, a gap in spectral coverage prevents us from determining the characteristics of the 1-micrometer absorption band accurately. The spectral slope as measured from 1.25 to 2.2 micrometers is 6-10%, which is modest compared to other S-type asteroids. The spectrum of this asteroid is similar to other near-Earth S-type asteroids that have been observed in the near-infrared wavelength region. On 4 January 1993, 4179 Toutatis was 0.182 AU from the Earth, and 1.158 AU from the Sun. At this solar distance, the thermal emission contributes substantially to the flux at 3 micrometers. The determination of thermal emission is complicated by the slow rotation rate and the irregular shape of this object that was revealed by radar observations [2]. Preliminary results suggest that no 3-micrometer absorption feature is present, indicating that this object is anhydrous. Using these spectral data, we will compare 4179 Toutatis to other S-type asteroids, both in the main belt and the near-Earth environment. References: [1] Pravec P.(1993) Personal communication. [2] Ostro S. J. (1993) paper presented at Hazards Due to Comets and Asteroids Conference.

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