Techniques d'observation spectroscopique d'astéroïdes

66 CHAPTER 4. SPECTRAL ANALYSIS TECHNIQUES
tel-00785991, version 1 - 7 Feb 2013
different types of observations, new taxonomic classes were defined. Historically, the most
widely used taxonomies are the following: Tholen [1984] and Barucci et al. [1987], which
used data from the Eight-Color Asteroid Survey [Zellner et al., 1985] together with thermal
albedo; Bus & Binzel [2002a], which used data from the SMASS2 survey; and DeMeo et al.
[2009], which is an extension of a previous taxonomy scheme into the near-infrared.
Statistical methods are used for defining taxonomic systems of asteroids. We point out two
of them, namely principal component analysis (PCA) and the G-mode clustering method.
Principal component analysis (PCA) is a method for reducing the dimensionality of a data
set of M variables, involving linear coordinate transformations to minimize the variance. The
first transformation rotates the data to maximize the variance along the first axis, known as the
principal component 1 (PC1), then along the second axis - the second principal component, and
so on. Overall, the new coordinates are ordered decreasingly in terms of the dispersion in the
principal components.
Bellow is the summary of Bus-DeMeo taxonomy in conformity with [DeMeo et al., 2009].
The prototype asteroids (specified by their number) of each class and a short description is
given.
A : 246, 289, 863 - Deep and extremely broad absorption band, first minimum near 1 µm; may
or may not have a shallow 2 µm absorption band; very highly sloped.
B : 2, 3200 - Linear, negatively sloping often with a slight round bump around 0.6 µm and/or
a slightly concave up curvature in the 1 to 2 µm region.
C : 1, 10, 52 - Linear, neutral visible slope often a slight rough bump around 0.6 µm; low but
positive slope after 1.3; may exhibit slight feature longword of 1 µm.
Cb : 191, 210, 785 - Linear with a small positive slope that starts around 1.1 µm.
Cg : 175 - Small positive slope that begins around 1.3 µm; pronounced UV dropoff.
Cgh : 106, 706, 776 - Small positive slope that begins around 1 µm; pronounced UV dropoff
similar to Cg; includes a broad, shallow absorption band centered near 0.7 µm similar to
Ch.
Ch : 19, 48, 49 - Small positive slope that begins around 1.1 µm; slightly pronounced UV
dropoff; includes a broad, shallow absorption band centered near 0.7 µm.
D : 1143, 1542, 3248 - Linear with very steep slope; some show slight curvature or gentle kink
around 1.5 µm.
K : 42, 579, 742 - Wide absorption band centered just longword of 1 µm; the fist maximum
and the minimum are sharply pointed; the walls of the absorption are linear with very little
curvature.
L : 236, 402, 606 - Steep slope in visible region leveling out abruptly around 0.7 µm; there is
often a gentle concave down curvature in the infrared with a maximum around 1.5 µm;
there may or may not be a 2 µm absorption feature.