Visible-Wavelength Spectroscopy of Asteroids

Since first becoming available for astronomical research in the early 1980s, charge-coupleddevice (CCD) spectrographs have had a profound impact on our ability to measure the spectralreflectance properties of asteroids. High signal-to-noise, low-resolution spectra, covering the visible-wavelength region from 0.4 to 1.0 μm, are now routinely obtained for asteroids much fainter than were measured during the Eight-Color Asteroid Survey. By recording the entire spectral range in a single exposure, some of the difficulties associated with multifilter photometry, arising from the inherent rotation of asteroids or from temporal variations in sky conditions, can be avoided. Studies involving CCD spectroscopy have resulted in the discovery of several absorption features in the spectra of asteroids and have provided new insights into the compositional nature of asteroid surfaces. Spectral surveys have also helped to refine our understanding of the orbital distributions of asteroid classes. We discuss the practical aspects of asteroid spectroscopy, focusing on observing procedures, data reduction techniques, and potential sources for uncertainty in the reduced spectra. We also review some of the applications of asteroid spectroscopy, and discuss how these observations have impacted the structure of asteroid taxonomy.