Techniques d'observation spectroscopique d'astéroïdes
Techniques d'observation spectroscopique d'astéroïdes
Techniques d'observation spectroscopique d'astéroïdes
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102 CHAPTER 6. SPECTRAL PROPERTIES OF NEAR-EARTH ASTEROIDS<br />
Relative Reflectance<br />
1.2<br />
1.1<br />
1<br />
0.9<br />
0.8<br />
0.7<br />
0.6<br />
(a)<br />
(188452) 2004 HE62<br />
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4<br />
Wavelength [um]<br />
Relative Reflectance<br />
1.1<br />
1<br />
0.9<br />
0.8<br />
0.7<br />
0.6<br />
0.5<br />
(b)<br />
Taxonomic classification for (188452) 2004 HE62<br />
Spectrum<br />
Sr<br />
Sv<br />
0.5 1 1.5 2 2.5<br />
Wavelength [um]<br />
0.26<br />
0.34<br />
tel-00785991, version 1 - 7 Feb 2013<br />
Relative Reflectance<br />
(c)<br />
0.24<br />
0.22<br />
0.2<br />
0.18<br />
0.16<br />
0.14<br />
Asteroid<br />
Relab sample<br />
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4<br />
Wavelength [um]<br />
Relative Reflectance<br />
(d)<br />
0.32<br />
0.3<br />
0.28<br />
0.26<br />
0.24<br />
0.22<br />
Asteroid<br />
Relab sample<br />
0.8 1 1.2 1.4 1.6 1.8 2 2.2<br />
Wavelength [um]<br />
Figure 6.4: a) The NIR spectrum of (188452) 2004 HE62 normalized to 1.25 µm; b) a polynomial fit for the<br />
spectrum of (188452) 2004 HE62 compared with the theoretical spectra of Sr and Sv types; c) the reflectance<br />
spectrum of (188452) 2004 HE62 and the closest fit resulting from meteorite spectra comparison - the L6 ordinary<br />
chondrite La Criolla; d) the de-reddened spectrum of (188452) 2004 HE62 and the closest matches resulting from<br />
meteorite comparison - the H6 ordinary chondrite Nanjemoy.<br />
on August 27, 2008 when the object had an apparent magnitude of 16.7.<br />
The spectrum of (188452) 2004 HE62 has two features around 1 and 2 µm: these are two<br />
deep absorption bands that are larger than for Sv-type meteorites but not so deep to be classified<br />
as one of the end members R or V. However, the classification is between the Sr and Sv classes<br />
in the Bus-DeMeo taxonomy (Fig. 6.4b). A visible spectrum would help to clarify the object’s<br />
classification. The spectral slope computed on the NIR part of the spectrum is 0.1167 µm −1 .<br />
Assuming an average albedo of 0.2 - typical for S-type objects, the diameter can be estimated<br />
to be ∼1 km.<br />
By comparing with data from the Relab database, this spectrum was found to be closely<br />
matched by the spectra of ordinary chondrite meteorites with low Fe, low metallic content,<br />
and high petrologic class (L6, L5, LL6) - Table 6.4. The best-fit solution was obtained with<br />
a spectrum of a particulate sample (0-150 µm) from the La Criolla meteorite (Sample ID:
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