Techniques d'observation spectroscopique d'astÃ©roÃ¯des

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106 CHAPTER 6. SPECTRAL PROPERTIES OF NEAR-EARTH ASTEROIDS found mainly in the outer regions of the asteroid belt. D-type asteroids are found in the extreme outer parts of the asteroid belt and among the Trojan objects [de Pater & Lissauer, 2010]. Their distribution in space provides insight into the temperatures, pressures and chemistry of the solar nebula. de Pater & Lissauer [2010] noted that D type asteroids are probably even more primitive than the C-types and it may have formed at even lower temperatures. Few things are known about the composition of D-type asteroids because few meteorites with similar spectral characteristics are available for study. One of the most interesting facts related to primitive asteroid is the fact that they are expected to contain organic materials 3 . In this section we describe two D-types asteroids which have orbits close to the Earth orbit. They are a valuable resource from the scientific point of view, since they are reachable for sample and return space mission. tel-00785991, version 1 - 7 Feb 2013 6.3.1 (5620) Jasonwheeler This object has the geometric albedo p v = 0.094 [Mueller et al., 2011]. It is an Amor-type asteroid with a diameter of 1.77 km [Mueller et al., 2011] and the synodic period of 5.307±0.001 hrs [Durkee, 2010]. The light-curve amplitude of 1.2 magnitude [Durkee, 2010] is indicative of an object with an elongated shape, or a binary system. Having ∆V = 6.974 km/s, this asteroid is a suitable target in terms of propulsion for a possible spacecraft mission. No other spectroscopic studies of this object were found in the literature. The NIR spectrum obtained on May 5, 2009 when the object had the apparent magnitude 16.5, is plotted in Fig. 6.7a. The MIT-SMASS online tool for taxonomy classified this object as belonging to D-class. With M4AST best-fit method, the spectrum is more similar to T-class (Fig 6.7b). In general, D- type asteroids have linear spectra with a very steep slope (greater than 0.38 µm −1 ) and display a slight curvature around 1.5 µm. On the other hand, T-types also have linear spectra with a steep gradient - between 0.25 and 0.38 µm −1 - that nevertheless gradually curves concavely downward. [DeMeo et al., 2009]. The spectrum of this asteroid has a steep slope in the 0.9 - 1.5 µm region and a slight curvature between 1.5 - 2.2 µm, though the classification is at the boundary between D-type and T-type. The overall NIR slope is 0.2504 µm −1 . Taking into account the low geometrical albedo when comparing with spectra from the Relab database, I found close spectral matches for this spectrum with CM2 carbonaceous chondrite meteorites(Table 6.4, Fig. 6.7d, 6.7e, 6.7f). In general, the CM2 meteorites are characterized by 30% levels of chondrules with grain sizes of≈300 µm, the absence of Fe-Ni alloys,and the presence of CAI (Ca -Al inclusions) [Dobrica, 2010]. The closest description of the spectrum is provided by a sample of particulates (0-75 µm) from the meteorite Mighei/Meghei (Sample ID: MR-MJG-108). Other spectra of CM2 carbonaceous chondrite meteorites that fit the Jasonwheeler NIR spectrum are those of powdered samples with particle sizes smaller than 3 https://www.oca.eu/MarcoPolo-R/
CHAPTER 6. SPECTRAL PROPERTIES OF NEAR-EARTH ASTEROIDS 107 tel-00785991, version 1 - 7 Feb 2013 Relative Reflectance (a) Relative Reflectance (c) Relative Reflectance 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 1.5 1.4 1.3 1.2 1.1 1 0.9 (5620) Jasonwheeler 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 Wavelength [um] 0.8 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 Wavelength [um] 0.08 0.075 0.07 0.065 0.06 0.055 0.05 0.045 0.04 Spectrum Poly. fit Slope Relative Reflectance (b) Relative Reflectance (d) Relative Reflectance 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.08 0.075 0.07 0.065 0.06 0.055 0.05 0.045 0.04 0.035 0.12 0.11 0.1 0.09 0.08 0.07 0.06 Taxonomic classification for (5620) Jasonwheeler Spectrum D T 0.5 1 1.5 2 2.5 Wavelength [um] Asteroid Relab sample 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 Wavelength [um] 0.035 0.03 Asteroid Relab sample 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 Wavelength [um] 0.05 Asteroid Relab sample 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 Wavelength [um] (e) (f) Figure 6.7: The NIR spectrum of (5620) Jasonwheeler; b) a polynomial fit for the spectrum of (5620) Jasonwheeler compared with the theoretical spectra of D and T types; c) estimation of thermal flux in the spectrum of (5620) Jasonwheeler - the dashed line indicates where a linearly extrapolated continuum would fall, the solid line shows the presence of thermal flux; d), e), f) the reflectance spectrum of (5620) Jasonwheeler and the closest three matches resulting from meteorite comparison: the CM2 carbonaceous chondrite Mighei/Meghei, the CM2 carbonaceous chondrite Cold Bokkeveld, and the CM2 carbonaceous chondrite ALH84029 [Popescu et al., 2011].
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OBSERVATOIRE DE PARIS ÉCOLE DOCTOR
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tel-00785991, version 1 - 7 Feb 201
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Résumé: L’objectif fondamental
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tel-00785991, version 1 - 7 Feb 201
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Acknowledgements tel-00785991, vers
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Dedicated to mygrandfather, IosifPo
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Contents Tables 22 Figures 27 I INT
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7.4.2 (3623) Chaplin . . . . . . .
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List of Tables 2.1 The emission lin
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List of Figures 1.1 A field obtaine
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5.8 Asteroid spectra and the best t
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1 Why asteroids? tel-00785991, vers
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CHAPTER 1. WHY ASTEROIDS? 33 tel-00
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CHAPTER 1. WHY ASTEROIDS? 39 the fi
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2 Why spectroscopy? spectrum. By ca
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CHAPTER 2. WHY SPECTROSCOPY? 45 0.4
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CHAPTER 2. WHY SPECTROSCOPY? 47 The
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CHAPTER 2. WHY SPECTROSCOPY? 49 0.6
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CHAPTER 2. WHY SPECTROSCOPY? 51 −
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CHAPTER 2. WHY SPECTROSCOPY? 53 tel
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Page 135 and 136: A The GuideDog and the BigDog inter
Page 137 and 138: B List of publications B.1 First Au
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Page 141 and 142: Bibliography Adams, J. B. 1974. Vis
Page 143 and 144: BIBLIOGRAPHY 143 Brunetto, R., Vern
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A&A 535, A15 (2011) Table 3. Summar
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A&A 535, A15 (2011) tel-00785991, v
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Band I center [um] 1.04 1.02 1 0.98
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A&A 544, A130 (2012) DOI: 10.1051/0
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M. Popescu et al.: M4AST - Modeling
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U.P.B. Sci. Bull., Series A, Vol. 7
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Applications of optical and infrare
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Mon. Not. R. Astron. Soc. 000, 000-
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Spectral properties of (854), (1333
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Vernazza P., Mothé-Diniz T., Baruc
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