TAXONOMIC CLASSIFICATIONS OF ASTEROIDS
David J. Tholen Institute for Astronomy 2680 Woodlawn Drive Honolulu, HI 96822
Since the last Asteroids book was published, there have been two taxonomic classification schemes developed and applied to the body of available color and albedo data (Tholen, 1984; Barucci et al., 1987). Asteroid taxonomic classifications according to these schemes are reproduced in the table. The Barucci et al. classifications have been copied directly from the paper they published in Icarus. Their classifications are based on a combination of eight-color photometry and IRAS albedos. The Tholen classifications are essentially the same as those supplied to the IRAS Asteroid Advisory Group in November, 1983, and as such, are not based on the IRAS albedos. This list consists of the classifications tabulated in Tholen (1984), but extended by a rigorous application of the classification scheme to those objects with UBV colors (Bowell et al., 1979), and a non-rigorous application to those objects with 24-color spectra (Chapman and Gaffey, 1979). A few of the classifications given here disagree with the ones given by Tholen (1984). These discrepancies are flagged in the Notes column. In some cases, the classifications of objects in the X and C spectral classes are based on unpublished albedos provided by Tedesco and Gradie. Although IRAS albedos are available that would permit the elimination of some classification ambiguities, caution is advised when applying IRAS albedos, because in many cases the IRAS fluxes have been overestimated, resulting in underestimated albedos.
Two differences between Tholen's 1984 list and this list are apparent. The letter X has been used to stand for E or M or P. Tholen (1984) used EMP, which could be misinterpreted as meaning E is most likely, M is next most likely, and P is least likely. Note that the E, M, and P classes are spectrally degenerate, so in the absence of albedo information, their similar spectra can be represented by a single letter. Also, the letter I has been introduced to stand for Inconsistent data. In Tholen (1984), 515 Athalia was given a stand-alone U classification, due to its S-type spectrum but uniquely low albedo. However, because of the desire to use U as only a suffix, the letter I was introduced.
The following notation appears in the classifications:
U suffix indicating an unusual spectrum; falls far from cluster center : suffix indicating noisy data :: suffix indicating very noisy data --- indicates data that are too noisy to permit classification (essentially all types would be allowed)
Due to popular demand, orbital group designations have been included in this table. The 2- or 3-letter abbreviations stand for the following groups:
ATE Aten APO Apollo AMO Amor MC Mars crosser HUN Hungaria PHO Phocaea GRI Griqua CYB Cybele HIL Hilda TRO Trojan
Explanatory notes and references are given in file TAXONOMY.NOT. This list was revised as of 1988 March 20 and therefore supercedes earlier tabulations.