Techniques d'observation spectroscopique d'astéroïdes

CHAPTER 7. SPECTRAL PROPERTIES OF MAIN BELT ASTEROIDS 117
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to be at the origin of Howardite-Eucrite-Diogenite meteorites. The structure of HED meteorites
is very close to mafic materials. Thus, the parent body of HED meteorites are supposed to have
experienced volcanism and metamorphism in the process of formation during the early Solar
System. The parent body of Vesta and vestoids underwent accretion, total melting, fractionation,
and differentiation during the first few million of years of Solar System formation [Keil,
2002].
The V-type asteroids are objects with reflectance spectra similar to the asteroid (4) Vesta
and to HED meteorites. These objects smaller in size than Vesta (commonly called ’vestoids’)
present spectral properties similar to this asteroid. Partly, the vestoids are identified as fragments
of Vesta, a result of the catastrophic collision who excavated material from the crust and
the mantle [Binzel & Xu, 1993] of (4) Vesta.
The V-type asteroids are mainly located in the population represented by the Vesta family,
and is considered to be the reservoir of HED meteorites. However, basaltic asteroids,
not yet considered members of Vesta family, are also located in the vicinity of the family
[Florczak et al., 2002, Duffard et al., 2004]. Data on V-type asteroids such as (1459) Magnya
are reported at different semi-major axis [Lazzaro et al., 2000, Roig & Gil-Hutton, 2006,
Duffard & Roig, 2009] and in the NEA population [Binzel et al., 2002]. This picture of V-
type asteroids supports the hypothesis of formation of several objects with basaltic crust in the
Main-Belt.
At present, hundreds of asteroids are classified as potentially V-type bodies, based on the
new photometric investigations. According to dynamical considerations some of these objects
possibly belong to the Vesta-family, while others seem to have no clear connection. Groundbased
observations allow to investigate the spectral properties and hence the mineralogical
composition of such asteroids.
(9147) Kourakuen is a main belt asteroid with an estimated diameter of 5.1 Km. Having
the semi-major axis a = 2.19 AU, eccentricity e = 0.108, and inclination i = 6.892 ◦ , this object
could not belong to Vesta family considering the dynamical criteria. However, its SDSS (Sloan
Digital Sky Survey) colors [Roig & Gil-Hutton, 2006] suggests a surface composition similar
to (4) Vesta (a V-type object). The cause could be a higher ejection velocity and a subsequent
dynamical evolution.
The spectrum of (9147) Kourakuen (Fig. 7.1a) has the characteristics of a V-type asteroid
[Popescu et al., 2012b]. In Bus-DeMeo taxonomy, V-type asteroids are characterized by a
very strong and very narrow 1 µm absorption feature and a strong 2 µm absorption feature
[DeMeo et al., 2009]. M4AST classify undoubtedly this spectrum as V-type. This agrees the
classification made via MIT-SMASS online tool. A similar result was found by de Sanctis et al.
[2011a] using a more noisy spectrum. The next two matches (the program always returns the
first three matches), Sv and Sr types have a larger matching error (Fig. 7.1b).
The solution given by all four methods for comparison with laboratory spectra shows that the