Techniques d'observation spectroscopique d'astéroïdes

38 CHAPTER 1. WHY ASTEROIDS?
heterogeneity of the protoplanetary disk at the time when the accretion of asteroids started.
These taxonomic classes emerged as more and more asteroids observations were available,
such that the modern taxonomies (e.g. Bus-DeMeo [DeMeo et al., 2009]) contain more than
20 classes.
From the point of view of their geological evolution, asteroids could be described by three
broad categories: primitive, partially melted, and differentiated. Primitive objects are mainly
made of silicates, carbon, and organics and some are similar to CI and CM meteorites. Olivine,
pyroxene and metal are the main constituents of asteroids partially melted, or at least thermally
altered. Remnants of disrupted differentiated bodies include basaltic types, nearly-pure olivine,
and metallic bodies, that represent pieces of the crust, mantle, and core [DeMeo, 2010].
1.4 Asteroid brightness and albedo
tel-00785991, version 1 - 7 Feb 2013
The apparent magnitude of asteroids depends on geometric parameters (Earth-object distance,
Sun-object distance and phase angle) and on the physical and optical properties of the body
(size and albedo). The absolute magnitude takes into account only the body intrinsic properties.
For asteroids it is defined as being the apparent magnitude if the body were at 1 AU from both
the observer and the Sun as seen at phase angle φ = 0. This is an analytical definition because
no geometrical point can satisfy the three conditions at the same time. It can be computed from
astrometric and photometric observations with the formula:
H = m v + 2.5·log Φ
r· ∆
(1.2)
where H is the absolute magnitude, m v is apparent magnitude, Φ is the phase integral (integration
of reflected light; a number in the 0 to 1 range), r is the heliocentric distance (measured in
AU), and ∆ is Earth-object distance (measured in AU) [Magrin, 2006].
The relation between the absolute magnitude and the body physical properties is:
log(p v· D 2 )=6.259−0.4·H (1.3)
where D is the diameter of the body expressed in km and p v is the geometrical albedo [Magrin,
2006].
The geometric albedo can be thought of as the amount of radiation reflected from a body
relative to that of a flat diffuse surface which is a perfect reflector at all wavelengths (called
Lambertian surface) [de Pater & Lissauer, 2010].
1.5 My contribution to asteroids discovery
My contribution to asteroids discovery can be divided in two parts: 1) the observing campaigns
in which I was involved and 2) the data-mining of archives for asteroids randomly appearing in