Data Set Overview
  =================
    This dataset provides taxonomic classifications of asteroids in
    each of five different systems: Tholen (1984, 1989) [THOLEN1984,
    THOLEN1989]; Barucci, et al. (1987) [BARUCCIETAL1987]; Tedesco,
    et al. (1989) [TEDESCOETAL1989]; Howell, et al. (1994)
    [HOWELLETAL1994], and Xu et al. (1995) [XUETAL1995].
 
    Asteroid taxonomy is the grouping of asteroids into a small number
    of classes whose members have similar spectral reflectance
    properties.  The classification efforts prior to 1990 used
    only the reflectivities between 0.3 and 1.1 microns and visual
    geometric albedos for this purpose (see Zellner et al. 1985
    [ZELLNERETAL1985] and Tedesco 1989 [TEDESCO1989]); more recently,
    infrared data extending to 2.5 microns were used for a new
    classification scheme (Howell et al. 1994 [HOWELLETAL1994]).
    Taxonomic classifications have also been made on the basis of
    spectra, as in the Small Main-belt Asteroid Spectroscopic Survey
    (SMASS) of Xu et al. (1995) [XUETAL1995].
 
    In this particular data set, the four parameter fields indicate
    which parameters were used to arrive at the classification for the
    corresponding asteroid in each of the first four taxonomies.  (The
    SMASS taxonomic classifications are all based on the SMASS spectra.)
    A number indicates the number of color indices used, the letter
    'G' indicates that a groundbased radiometric albedo was also used,
    and the letter 'I' indicates that an IRAS radiometric albedo was
    used.  The letter 'S' indicates that the classification is
    based on a medium resolution spectrum published by Chapman and
    Gaffey (1979) [CHAPMAN&GAFFEY1979A].
 
    The Tholen (1984) [THOLEN1984] taxonomy used Eight-Color Asteroid
    Survey color  indices (Zellner et al. 1985 [ZELLNERETAL1985]),
    ground-based visual geometric albedos where available, and a minimal
    tree clustering algorithm. The Tholen (1989) [THOLEN1989] extension
    incorporated UBV color indices and some medium resolution
    spectrophotometry. The Barucci et al. (1987) [BARUCCIETAL1987]
    taxonomy also used Eight-Color data, but only those for which a
    complete set of seven color indices were available, IRAS visual
    geometric albedos, and a G-mode cluster analysis method. The Tedesco
    et al. (1989) [TEDESCOETAL1989] taxonomy used only the u-v and
    v-x color indices from the Eight-Color Asteroid Survey, mostly IRAS
    visual geometric albedos (but a few ground-based albedos for
    particularly interesting cases), and a stereoscopic viewing method
    for identifying clusters.  The Howell et al. (1994) [HOWELLETAL1994]
    taxonomy is based on a combination of Eight-Color and 52-color
    (Bell et al. 1988 [BELLETAL1988]) data, resampled at 65 points to
    provide more uniform wavelength sampling, and a neural network
    cluster identification method, though in eight cases, a visual
    geometric albedo was used to distinguish between two or more
    possible classifications.
 
    The data set contains entries for 1198 objects.  Each of the five
    taxonomies represented in this data set produced classifications
    for a subset of these objects:
 
      Tholen (1984, 1989)      978 objects
      Barucci et al. (1987)    438 objects
      Tedesco et al. (1989)    357 objects
      Howell et al. (1994)     112 objects
      Xu et al. (1995)         221 objects
 
    Six objects not classified by Tholen have some spectral
    reflectance data available, but the data were deemed too noisy
    to produce a classification.  Their '---' entries in the
    classification table serve simply to call attention to the fact
    that some spectral reflectance data do exist for these objects.
 
    Nine asteroids in the Eight-Color Asteroid Survey paper (Zellner
    et al. 1985 [ZELLNERETAL1985]) had not yet been numbered at the
    time of publication, but they are all numbered now and are
    identified by their number in this data set.  They are cross-
    referenced by their publication designation here:
 
      1979 VA      (4015) Wilson-Harrington
      1980 WF      (4688)
      1981 LA      (3169) Ostro
      1981 QA      (3102) Krok
      1981 QF2     (3123) Dunham
      1981 VB      (3124) Kansas
      1982 DV      (3288) Seleucus
      1982 RA      (3199) Nefertiti
      1982 XB      (3757)
 
 
  Modification History
  ====================
    The asteroid taxonomy data set was first reviewed and ingested in
    1993, and was updated in 1997 to include the neural net taxonomy of
    Howell et al. (1994) [HOWELLETAL1994].  It was updated in 1999 to
    include the taxonomic classifications of the SMASS survey, Xu et al.
    (1995).
 
 
  Parameters
  ==========
    The data table includes taxonomic classifications and the parameters
    used to derived that classification in each of the Tholen, Barucci,
    Tedesco, and Howell systems.

Review
  ======
    This data set underwent external peer review on April 9, 1999.
 
 
  Limitations
  ===========
    Four entries have a notation in the comment field.  The
    classification for (152) Atala in the original reference is based
    on data that have been found to be inconsistent with other
    observations.  The current belief is that this object may have
    been misidentified during the course of the Eight-Color Asteroid
    Survey, therefore the Tholen classification has been change to 'I'
    to reflect inconsistent data; the Howell et al. (1994)
    [HOWELLETAL1994] classification reflects the inconsistency.
 
    The classifications for (2151) Hadwiger and (2422) Perovskaya are
    based on UBV colors published by Bowell et al. (1979)
    [BOWELLETAL1979], where they are identified as 1975 EA and 1975 GB,
    respectively.  These designations are not the principal provisional
    designations (which are actually 1977 VX and 1968 HK1, respectively),
    therefore the proper identity of these objects in the original
    Bowell et al. table will not be obvious unless a listing of asteroid
    identifications is consulted.
 
    The classification for 1975 RC is also based on UBV colors
    published by Bowell et al. (1979) [BOWELLETAL1979], where it is
    identified as 1975 U2, which is not a proper provisional designation.
    Efforts to determine the correct identity of this object revealed
    that 1975 U2 appears to be a designation assigned by C.-I. Lagerkvist
    for his own personal use (prior to his learning of the formal
    provisional designation), but it was apparently also communicated
    to E. F. Tedesco, the observer of the colors.  There was
    sufficient confusion generated by the investigation, however, that
    potential users of this classification should be warned that the
    identification of 1975 U2 as 1975 RC may be incorrect.