An extension of the Bus asteroid taxonomy into the near-infrared

The availability of asteroid spectral measurements extending to the near-infrared, resulting from the development of new telescopic instruments (such as SpeX [Rayner, J.T., and 7 colleagues, 2003. Astron. Soc. Pacific 115, 362–382]), provides a new basis for classifying asteroid reflectance spectra. We present an asteroid taxonomy classification system based on reflectance spectrum characteristics for 371 asteroids measured over the wavelength range 0.45 to 2.45 μm. This system of 24 classes is constructed using principal component analysis, following most closely the visible wavelength taxonomy of Bus [Bus, S.J., 1999. Ph.D. thesis, Massachusetts Institute of Technology], which itself builds upon the system of Tholen [Tholen, D.J., 1984. Ph.D. thesis, University of Arizona]. Nearly all of the Bus taxonomy classes are preserved, with one new class (Sv) defined. For each class we present boundary definitions, spectral descriptions, and prototype examples. A flow chart method is presented for classifying newly acquired data spanning this wavelength range. When data are available only in the near-infrared range (0.85 to 2.45 μm), classification is also possible in many cases through an alternate flow chart process. Within our sample, several classes remain relatively rare: only 6 objects fall into the A-class; 349 Dembowska and 3628 Boznemcova reside as the only objects in their respective R- and O-classes. Eight Q-class objects are all near-Earth asteroids. We note 1904 Massevitch as an outer main-belt V-type while 15 other V-type objects have inner main-belt orbits consistent with an association with Vesta.