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[108.05] 0.7~\mum Observations of Hydrated Central Belt Asteroids

A. M. Soderberg (NAIC Arecibo Observatory, Bates College), E. S. Howell (NAIC Arecibo Observatory)

We investigate the rotational variability of the 0.7~\mum Fe²+ and Fe³+ oxidized iron absorption feature in low albedo asteroid reflectance spectra. A correlation has been reported between the presense of this weak transition band and the deep water of hydration feature at 3.0~\mum. This strong water absorption band indicates aqueous alteration of the asteroid resulting in hydrated materials on the surface. We coordinate spectroscopy at 0.5--0.9~\mum using the 2.1m at McDonald Observatory with observations at 3.0~\mum from the NASA Infrared Telescope Facility to test the correlation reported. Previous inconsistencies between the visible band and the 3.0~\mum band observations may be the result of rotational phase offsets in the dataset. This implies a nonhomogenous distribution of hydrated materials on the asteroid surface. Among the 7 asteroids studied in detail to date, we find that 3 show rotational variability at 0.7\mum. Two additional objects have shown variability in past observations at different observing geometries. This indicates that rotational variability is relatively common. We report coordinated observations (same rotation phase) for low albedo central belt asteroids. Results demonstrate that the correspondence between these two absorption bands is more complex than originally suggested.