A spectroscopic survey of D-type asteroids

Abstract

We present CCD spectra of 19 asteroids previously classified as D-type covering the wavelength range 3500≤λ≤9600 A. A comparison with previously published photometric data shows excellent agreement. No small-scale absorption features are seen, but two asteroids (102 Miriam and 914 Palisana) exhibit large-scale absorption (Δλ∼2000 A) characteristic of phyllosilicates and are confirmed as belonging to the C or P groups. A heliocentric colour gradient recently reported is presumed to be caused by the presence of silicates on asteroids lying within the main-belt, but it is unknown whether this material is inherent to the asteroid or has been deposited there by impacts