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[7P.08] The 0.43-\micron Absorption Feature in Reflectance Spectra of Low-Albedo Asteroids

K. S. Jarvis (Lockheed-Martin), F. Vilas (NASA JSC), M. J. Gaffey (RPI), A. Fitzsimmons (Queen’s U., Belfast)

A 0.43-\micron absorption feature attributed to the ⁶A₁\longrightarrow⁴A₁, ⁴E(G) Fe³⁺spin-forbidden crystal field transition has been identified in the reflectance spectra of some low-albedo asteroids (Vilas et al., 1993, Allen et al., 1996). Similar absorptions have been seen in terrestrial minerals such as the iron sulfate jarosite, though a strong UV IVCT absorption masks the 0.43-\micron absorption feature in many minerals. We have reflectance spectra of over 50 asteroids covering 0.43-\micron. Of these spectra, one-third of the asteroids have data taken on multiple dates, illustrating the repeatability of the feature. These spectra emphasize (but are not exclusively) low-albedo asteroids located in the outer part of the main asteroid belt and the outer asteroid belt (\leq5.2 AU). This weak absorption feature is centered near 0.43-\micron, overlying the solar G line also centered here, however the solar G line is narrower than the 0.43-\micron absorption feature. We are evaluating the spectra to confirm and refine the presence of the 0.43-\micron absorption feature and to insure it is not confused with residual absorptions that could be created by incomplete removal of the solar G line. Any correlation of the 0.43-\micron absorption feature with the 0.7-\micron absorption feature attributed to an Fe²⁺\longrightarrow Fe³⁺ charge transfer band in oxidized iron in phyllosilicates, and with asteroid class, will be presented. [This research is supported by the NASA Planetary Astronomy Program (FV) and by NASA Planetary Geology and Geophysics Grant NAGW-642 (MJG).]