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

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98 CHAPTER 6. SPECTRAL PROPERTIES OF NEAR-EARTH ASTEROIDS (8567) 1996 HW1 Taxonomic classification for (8567) 1996 HW1 1.2 1.2 Relative Reflectance (a) 1.15 1.1 1.05 1 0.95 0.9 0.85 0.8 0.75 0.7 V NIR 0.5 1 1.5 2 2.5 Wavelength [um] Relative Reflectance (b) 1.1 1 0.9 0.8 0.7 0.6 Spectrum S Sq 0.5 1 1.5 2 2.5 Wavelength [um] tel-00785991, version 1 - 7 Feb 2013 Relative Reflectance (c) 0.22 0.21 0.2 0.19 0.18 0.17 0.16 0.15 0.14 0.13 Asteroid 0.12 Relab sample 0.5 1 1.5 2 2.5 Wavelength [um] Relative Reflectance (d) 0.34 0.32 0.3 0.28 0.26 0.24 Asteroid Relab sample 0.5 1 1.5 2 2.5 Wavelength [um] Figure 6.2: a) The visible [Vernazza, 2006] and the NIR spectra of (8567) 1996 HW1; b) a polynomial fit of the V+NIR spectrum of (8567) 1996 HW1 compared with the theoretical spectra of S and Sq types; c) reflectance spectrum of (8567) 1996 and the closest match resulting from the meteorite comparison - the LL4 ordinary chondrite Hamlet; d) de-reddened spectrum of (8567) 1996 HW1 and the closest match resulting from meteorite comparison -the LL6 ordinary chondrite Cherokee Springs. (Fig. 6.2a) before analyzing the composite spectrum. Using the taxonomic classification tool from the MIT-SMASS, this NEA is classified as an S-type with the spectral slope 0.2245 µm −1 . Using the M4AST approach, it can be found that an Sq type provides a closer fit spectrum than an S (Fig. 6.2b). Sq type is at the transition between S and Q classes with two absorption bands around 1 µm and 2 µm that are more shallow than for Q-type [DeMeo et al., 2009]. Comparing the features for the two considered spectral types with a polynomial fit of the spectrum, it can be observed that an Sq type matches more closely the obtained data than an S type. Since there are no measurement of the albedo for this object, assuming a value of 0.20 as typically found for the albedo of S-type asteroids [Fulchignoni et al., 2000], the diameter can be estimated to be ≈ 2.5 km. The spectrum from the Relab sample that provides the closest fit is a particulate ground sorted (0-125 µm) Hamlet meteorite (sample ID: OC-TXH-002-C), an ordinary chondrite with
CHAPTER 6. SPECTRAL PROPERTIES OF NEAR-EARTH ASTEROIDS 99 Table 6.4: Summary of results obtained by matching the asteroid spectra and de-reddened asteroid spectra with spectra from the Relab database. The comparison was made using a χ 2 method and a selection of the obtained results was done based on spectral features (band, band-gap, concavity) positions, and albedo values. For (5620) Jasonwheeler, a de-reddening model was not applied tel-00785991, version 1 - 7 Feb 2013 Matching results for asteroid spectra Spectrum Meteorite Sample ID Type Texture Size [ µm] (1917) Cuyo Dhajala LM-LAM-026 OC/H3-4 Thin Section - (8567) 1996 HW1 Hamlet OC-TXH-002-C OC/ LL4 Particulates 0-125 (16960) 1998 QS52 Saratov MB-CMP-028-H OC/L4 Particulates 0-370 Homestead MR-MJG-048 OC/L5 - - Hamlet 1 MR-MJG-069 OC/LL4 - - (188452) 2004 HE62 La Criolla MH-FPF-050-B OC/L6 Particulates 0-150 Cherokee Springs OC-TXH-001-A OC/LL6 Chip - Wold Cottage MH-FPF-064 OC/L6 Particulates - 2010 TD54 Saratov MB-CMP-028-B OC/L4 Particulates 10-45 Mirzapur TB-TJM-111 OC/L5 Particulates 0-150 Rio Negro TB-TJM-081 OC/L4 Particulates 0-150 Matching results for de-reddened asteroid spectra (1917) Cuyo Lancon MR-MJG-033 OC/H6 - - Collescipoli MR-MJG-030 OC/H5 - - Ehole TB-TJM-074 OC/H5 Particulates 0-150 (8567) 1996 HW1 Cherokee Springs TB-TJM-090 OC/LL6 Particulates 0-150 Hedjaz OC-TXH-016-C OC/L3-6 Particulates 0-125 Ensisheim TB-TJM-092 OC/LL6 Particulates 0-150 (16960) 1998 QS52 Hamlet 1 MR-MJG-069 OC/LL4 - - Gruneberg MR-MJG-040 OC/H4 - - (188452) 2004 HE62 Nanjemoy MR-MJG-034 OC/H6 - - Olmedilla de Alarcon MR-MJG-075 OC/H5 - - MAC88119.9 MB-TXH-044 OC/H5 Slab 0 2010 TD54 Gruneberg MR-MJG-040 OC/H4 - - Queen’s Mercy MR-MJG-035 OC/H6 - - Ochansk MR-MJG-027 OC/H4 - - a low level content of Fe and metal - LL4 (Table 6.4, Fig. 6.2c). The asteroid spectrum in the region 1.6 -2.5 µm is shallower than that of the meteorite spectrum, which could be explained by considering space-weathering effects. Using the space weathering model of Brunetto et al. [2006], it can be found that C s = -0.258 µm. Modelling this with a damage parameter due to the solar-wind ion irradiation the number of displacements per cm 2 can be found as d = 1.08×10 19 , showing that it has experienced an appreciable amount of space weathering. By removing the exponential continuum and comparing again with Relab meteorite spectra, the closest matches are also ordinary chondrite (LL6, L3-6 types) spectra with a low metal, low Fe content. The meteorite spectra that provide the closest fit of the de-reddened spectrum of this asteroid are those of: Cherokee Spring (Fig. 6.2d), Hedjaz,and Ensisheim (Table 6.4). The Relab samples of these meteorites are particulates sorted in order of their sizes, which are smaller than 150 µm.
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OBSERVATOIRE DE PARIS ÉCOLE DOCTOR
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Résumé: L’objectif fondamental
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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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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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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
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BIBLIOGRAPHY 149 Popescu, M., Birla
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A&A 535, A15 (2011) Table 1. Log of
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A&A 535, A15 (2011) Table 3. Summar
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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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