

                  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in the X and C spectral classes are based on unpublished albedos provided by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.
